Innate Immunity
1. A 58-year-old white man presents with weight loss, night sweats, and dyspnea. On examination, the patient appears chronically ill and is pale. Laboratory testing reveals leukocytosis, anemia, and thrombocytopenia. A bone marrow biopsy with aspirate is performed, and a diagnosis of acute myelogenous leukemia is confirmed. In counseling the patient about chemotherapy, you inform him that he is going to be at increased risk for infections and that a major source of infection will be his own gastrointestinal tract.
Which of the following statements regarding the innate immune system and the epithelial barrier in the GI tract is false?
A. Lectins found in secretions bind sugars on pathogens and activate the lectin pathway of complement activation
B. Granulocytes marginate in small blood vessels throughout much of the barrier tissues and are available for rapid recruitment to a possible site of infection
C. Mucus itself is a protective barrier that traps organisms and debris
D. Secretions on the epithelial barrier concentrate complement in such a way that the concentration of complement in secretions is higher than the concentration in plasma
E. Monocytes are present in secretions and in most tissues, where they phagocytose unwanted microbes
Key Concept/Objective: To understand the basic principles of the innate immune system
The innate immune system is particularly active at the interface between the environment and the surfaces of the body that are lined with epithelial cells—namely, the skin and the GI, genitourinary, and sinopulmonary tracts. Intact physical barriers are critically important for preventing infections. In addition to the epithelial barrier itself, the fluids in these tracts contain mucus, natural antibodies (IgG and IgA), a complement system, and lectins. The complement system in secretions is present at about 10% to 20% of the concentration found in plasma. The lectins in these secretions bind sugars on pathogens and thereby activate the lectin pathway of complement activation. Granulocytes marginate in small blood vessels throughout much of these barrier tissues and are available for rapid recruitment to a possible site of infection. Monocytes/macrophages are also present in secretions and in most tissues, where they phagocytose unwanted microbes. Mucus itself is a protective film that traps organisms and debris; it also contains antibacterial substances. (Answer: D— Secretions on the epithelial barrier concentrate complement in such a way that the concentration of complement in secretions is higher than the concentration in plasma)
2. A 26-year-old female patient has had recurrent infections with pyogenic organisms. She has a follow-up appointment with you today to discuss her options. You remember that complement is a major mechanism by which the innate immune system can act and that certain complement deficiencies can cause disease.
Which of the following statements regarding the complement cascade is false
A. The alternative pathway requires antibodies for initiation
B. The three complement pathways are the classical pathway, the alternative pathway, and the lectin pathway
C. The membrane attack complex (MAC) allows perforation via channel or pore formation into the foreign membrane
D. C3 degradation occurs spontaneously all the time, and C3 fragments bind to host cells and foreign cells; however, regulatory proteins on host cells protect cells by inactivating such fragments
Key Concept/Objective: To understand the complement system and its pathways
The complement system lies at the interface between innate and acquired immunity. As a key component of innate immunity, it promotes the inflammatory response and attacks and destroys foreign substances. Inherited deficiencies of components in the activating cascade predispose to infectious diseases, primarily of a pyogenic type; surprisingly, such deficiencies also predispose to autoimmunity, especially systemic lupus erythematosus (SLE). The early part of the complement system is divided into three branches: the antibody-initiated classical pathway; the antibody-independent (i.e., innate) alternative pathway; and the more recently described lectin pathway. Although each branch is triggered differently, all share the common goal of depositing clusters of C3b on a target. This deposition results in the assembly of a common lytic mechanism called the MAC or C5b-9. The alternative pathway is an ancient pathway of innate immunity. Unlike the classical pathway, the alternative pathway does not require antibody for initiation. Rather, the natural breakdown (low-grade turnover) of plasma C3 via spontaneous cleavage of a highly reactive thioester bond allows such C3 to attach to any nearby host or foreign surface. Regulatory proteins on host cells protect cells by inactivating such fragments. However, foreign membranes usually do not possess such inhibitors, so amplification (the feedback loop of the alternative pathway) becomes engaged. As a further assault against a pathogen, the alternative pathway assembles the MAC. In this case, the C5 convertase (C3bBbC3bP) cleaves C5 to C5b. This promotes assembly of C6 + C7 + C8 and multiple C9s to allow perforation (channel or pore formation) into the foreign membrane. (Answer: A—The alternative pathway requires antibodies for initiation)
3. A 32-year-old African-American woman with systemic lupus erythematosus (SLE) presents to your office for an examination. Her disease course has been complicated by hemolytic anemia, renal disease, synovitis, and rash. Her current regimen consists of low-dose prednisone. During her visit, she says she has done some research on the Internet and wants to know if her SLE is caused by a problem with complement.
Which of the following statements regarding complement is false?
A. Almost all inherited complement deficiencies are inherited as autosomal dominant traits
B. Immune complexes can lodge in blood vessel walls and activate complement to produce synovitis, vasculitis, dermatitis, and glomerulonephritis
C. A deficiency of complement regulatory proteins usually causes excessive activation
D. Deficiencies of early components (e.g., C1q, C1r/C1s, C4, and C2) predispose to SLE, whereas deficiencies of C3, MBL, or MAC components lead to recurrent bacterial infections
Key Concept/Objective: To understand the basic principles of complement and disease states
The pathophysiology of many inflammatory diseases involves the synthesis of autoantibodies and the presence of excessive quantities of immune complexes. If immune complexes lodge in blood vessel walls, they may activate complement to produce synovitis, vasculitis, dermatitis, and glomerulonephritis. Similarly, a powerful complement barrage may follow ischemia-reperfusion injury as the alternative pathway elicits C3b deposition on the damaged tissue, which is regarded as foreign. Complement component deficiencies, although rare, predispose to autoimmune diseases (e.g., SLE) and bacterial infections. Deficiencies of complement regulatory proteins allow for excessive activation. These conditions are usually inherited as autosomal codominant traits (i.e., recessive), with the exception of C1-Inh (autosomal dominant) and properdin (X-linked). Deficiencies of early components (e.g., C1q, C1r/C1s, C4, and C2) predispose to SLE, whereas deficiency of C3, MBL, or MAC components leads to recurrent bacterial infections. (Answer: A—Almost all inherited complement deficiencies are inherited as autosomal dominant traits)
For more information, see Atkinson JP, Liszewski MK: 6 Immunology/Allergy: II Innate Immunity. ACP Medicine Online (www.acpmedicine.com). Dale DC, Federman DD, Eds. WebMD Inc., New York, June 2004
Histocompatibility Antigens/Immune Response Genes
4. A 43-year-old man comes for a routine follow-up. Several months ago, the patient presented for evaluation of weight loss, rash, and iron-deficiency anemia. You diagnosed him as having celiac disease. The patient states he is doing well on his gluten-free diet. He has gained 10 lb since his last visit 2 months ago. Today his anemia is also seen to have improved. You remember that celiac disease results from immune dysregulation, and you are stimulated to learn more about adaptive immunity.
Which of the following statements regarding the antigens of the major histocompatibility complex
(MHC) is false?
A. There are two structural types of MHC molecules, called class I and class II
B. Clonally determined antigen receptors on B cells recognize and bind to specific peptide-MHC complexes
C. MHC molecules act by binding peptide fragments of antigens that have been processed in specialized antigen-presenting cells
D. Class II antigens are encoded by the HLA-D region
Key Concept/Objective: To understand MHC molecules
There are two structural types of MHC molecules, called class I and class II. The molecules of both classes are active in antigen recognition and help focus immune defenses during invasions from the microbial world. They are also engaged in the communication that occurs between cells during the immune response. MHC molecules act by binding peptide fragments of antigens that have been processed in specialized antigen-presenting cells. Clonally determined antigen receptors on T cells then recognize and bind to specific peptide-MHC complexes, setting into motion the appropriate immune response. Class II antigens are encoded by the HLA-D region, which is divided into at least three subregions: HLA-DP, HLA-DQ, and HLA-DR. Class I heavy chains are the gene products of three MHC loci, designated HLA-A, HLA-B, and HLA-C. (Answer: B—Clonally determined antigen receptors on B cells recognize and bind to specific peptide-MHC complexes)
5. A 22-year-old man presents to establish primary care. He has been healthy most of his life, but he does have type 1 diabetes mellitus, which he reports has been under very good control. He informs you that when last measured, his hemoglobin A1C value was 5.2%. He has no history of retinopathy or neuropathy, and he states that he saw his ophthalmologist 6 weeks ago. The patient has had protein in his urine, and he takes an angiotensin-converting enzyme (ACE) inhibitor. He asks you, “What causes type 1 diabetes?” You explain that the underlying problem is that his body has mistaken its own pancreatic molecules for foreign molecules. Later that day, you decide to read further on adaptive immunity.
Which of the following statements regarding antigen processing and presentation is false?
A. Class I molecules are expressed on virtually all tissues and are important in the recognition of virally infected cells
B. Class II molecules are expressed on a limited variety of cells known as antigen-presenting cells
C. MHC molecules first bind peptide fragments after the MHC molecules reach the cell surface
D. Exogenous proteins are taken up by endosomes or lysosomes, where they are catabolized; their peptides are then bound to MHC class II molecules
Key Concept/Objective: To understand the processing of foreign proteins and their relationship to the MHC system
The breakdown of protein molecules into peptide fragments is an important part of the process by which antigens are presented to T cells and other immune effector cells. MHC molecules come to the cell surface with peptides already bound. Proteins are first degraded internally, and the peptide fragments are bound to MHC class I and MHC class II molecules within the cell. Class I molecules are expressed on virtually all tissues. Virally infected cells are recognized principally by class I-restricted T cells, usually those with a cytotoxic function. In contrast, class II-directed T cells are restricted to antigen-presenting cells of the immune system (i.e., B cells, macrophages, dendritic cells, or Langerhans cells) that are principally concerned with defense against external infectious agents. Exogenous and endogenous antigens reach the cell surface by different pathways. Exogenous proteins are taken up into endosomes or lysosomes, where they are catabolized. Peptides from exogenous proteins are generally bound to MHC class II molecules, and the class II–peptide complexes are then brought to the surface for presentation to T cells. Peptides from endogenous proteins (e.g., secretory proteins or products of viral infection) appear to be complexed in the endoplasmic reticulum to MHC class I molecules. (Answer: C—MHC molecules first bind peptide fragments after the MHC molecules reach the cell surface)
6. A 23-year-old primigravida who is known to be Rh-negative is told by her obstetrician that she needs a medication to prevent complications (i.e., erythroblastosis fetalis) of her next pregnancy. She wonders why she should be using this medication.
Which of the following immunologic responses is prevented by the use of anti–Rh-positive antibodies (RhoGAM)?
A. Primary immune response to antigen
B. Secondary immune response (anamnestic or booster response)
C. Somatic hypermutation
D. Class switch recombination
Key Concept/Objective: To understand the genesis and prevention of the secondary immune response
If an antigen is encountered a second time, a secondary response (also called an anamnestic or booster response) occurs because of the existence of memory B cells. Administration of RhoGAM to the mother at the time of delivery prevents the fetal red blood cells, which are Rh positive, from generating a primary response in the Rh-negative mother, thus decreasing significantly the possibility of an anamnestic response in future pregnancies. Both IgM and IgG titers rise exponentially, without the lag phase seen in the primary response. Whereas the peak IgM level during the secondary response may be the same as, or slightly higher than, the peak IgM level during the primary response, the IgG peak level during the secondary response is much greater and lasts longer than the peak level during the primary response. This variation in response is an apt illustration of immunologic memory and is caused by a proliferation of antigen-specific B cells and helper T cells during the primary response. The primary immune response characterizes the first exposure to antigen and is largely IgM mediated; later production of IgG is not as great in magnitude or duration as that produced during the secondary response. Somatic hypermutation, class switch recombination, and immunoglobulin class switching are all mechanisms involved in producing the appropriate immunoglobulin with the highest antigen specificity. (Answer: B—Secondary immune response [anamnestic or booster response])
7. A 48-year-old woman with severe rheumatoid arthritis (RA) is advised by a rheumatologist to consider a novel antibody, because her arthritis is not responding to therapy with methotrexate. She asks you about this new medication.
Of the following, which is the therapeutic target of approved engineered human monoclonal antibodies in the management of RA?
A. Interleukin-6 (IL-6)
B. IL-10
C. Tumor necrosis factor–a (TNF-a)
D. IL-1
Key Concept/Objective: To understand the clinical application of engineered monoclonal antibodies
Humanized monoclonal antibodies to TNF-a have been used successfully in the treatment of Crohn disease and RA. These monoclonal antibodies are indicated for patients with moderate to severe RA that is not responsive to methotrexate or for patients in whom methotrexate toxicity has occurred. IL-1 is a proinfammatory cytokine implicated in the pathogenesis of RA. There is an FDA-approved IL-1 receptor antagonist, but it is not a monoclonal antibody. Monoclonal antibodies against IL-6 have been used in clinical trials, but they failed to demonstrate clinical benefit and are not approved for use at this time. IL-10 is an endogenous inhibitor of IL-1, TNF-a, and interferon gamma; attempts at using IL-10 in the treatment of RA failed. Clinical therapeutics utilizing monoclonal antibodies will expand with the emergence of new understanding of the underlying pathophysiology of various disease processes. (Answer: C—Tumor necrosis factor–a [TNF-a])
For more information, see Carpenter CB, Terhorst CP: 6 Immunology/Allergy: V Adaptive Immunity: Histocompatibility Antigens and Immune Response Genes. ACP Medicine Online (www.acpmedicine.com). Dale DC, Federman DD, Eds. WebMD Inc., New York, July 2004
Immunogenetics of Disease
8. A 42-year-old white man presents to primary care clinic complaining of fatigue. Physical examination is significant for splenomegaly. Laboratory data reveal a leukocytosis with 3% blasts and numerous immature cells of the granulocytic lineage, and a low leukocyte alkaline phosphatase (LAP) level. Cytogenetic analysis reveals the Philadelphia chromosome [t(9;22)], and a diagnosis of chronic myelogenous leukemia (CML) is made. Subsequently, the patient seeks evaluation for allogeneic stem cell transplantation. During your discussion with him, you explain the importance of human leukocyte antigen (HLA) matching of donor and recipient to reduce the incidence of graft-versus-host disease.
Which cluster of highly polymorphic genes encodes these cell surface markers?
A. The cytokine cluster loci
B. The major histocompatibility complex (MHC)
C. The cytokine histocompatibility complex
D. The chemokine histocompatibility cluster
Key Concept/Objective: To understand that MHC encodes HLA
The MHC—so called because of its prominent role in rejection of allogeneic tissue—is a primary barrier to transplantation of solid organ, tissue, and hematopoietic stem cells. This closely linked cluster of highly polymorphic genes, grouped on the short arm of chromosome 6, encodes cell surface molecules (e.g., HLA). The normal role of the MHC is presentation of endogenous and exogenous peptide antigen fragments to T lymphocytes, thereby initiating an immune response against the molecule (or pathogenic organism) from which the peptide was derived. The extreme variability of molecular structure in the MHC antigens permits a wide range of different peptides to be presented by autologous human antigen-presenting cells, although individual subjects may have a specific repertoire of MHC antigens that do not present certain antigens effectively. The focused immunogenicity of MHC molecules and the variability of these molecules among individuals render them prominent targets for the immune response in the context of solid organ and bone marrow transplantation. In cases in which live allogeneic cells are the target of the immune response, the apparent target is the nonself MHC molecule itself. Freedom from rejection and, in the case of bone marrow transplantation, graft-versus-host disease is improved with HLA matching of donor and recipient. (Answer: B—The major histocompatibility complex [MHC])
9. A 72-year-old woman with emphysema presents for evaluation for possible lung transplantation.
Laboratory evaluation for cytokine polymorphism of the transforming growth factor (TGF) gene, considered as homozygosity for TGF-a, is associated with graft fibrosis in 93% of lung transplant recipients. TGF-a has two well-studied dimorphic positions within the leader sequence of the gene whose variants are found in concert with one another.
What designation is given to variants at polymorphic positions that display this relationship?
A. Hardy-Weinberg equilibrium
B. Allelic equilibrium
C. Linkage disequilibrium
D. Allelic disequilibrium
Key Concept/Objective: To understand the relationships between polymorphic nucleotide positions in or near an expressed gene on the same chromosome with regards to whether they occur in populations independently of one another
There can be multiple polymorphic nucleotide positions in or near an expressed gene on the same chromosome. In such cases, it is desirable to know whether specific variants at each of the polymorphic positions are independent of the variants at the other positions. If examination of a population shows that the variants at the different positions occur independently of one another, the system is said to be in Hardy-Weinberg equilibrium. If certain variants at one of the positions are statistically associated with specific variants at another of the linked positions, the system is said to exhibit linkage disequilibrium. Hardy-Weinberg equilibrium can be reestablished over many generations through recombination events. The closer the polymorphic loci are to each other on the chromosome, the less likelihood there is of a recombination, and the specific alleles at the two linked loci are more likely to be inherited en bloc as a haplotype. (Answer: C—Linkage disequilibrium)
10. A clinical investigator studying the genetic predisposition of individuals with a family history of diabetes mellitus to develop clinical diabetes discovers a novel genetic polymorphism in a cohort of such patients.
Which of the following describes a mutation whose frequency becomes established at more than 1%
to 2% of the population?
A. A haplotype
B. An allele
C. A unique polymorphism
D. A single nucleotide polymorphism
Key Concept/Objective: To understand that genetic polymorphisms with a frequency of more than 1% to 2% are alleles
The fundamental basis of genetic polymorphism in a population is variation of the nucleotide sequence of DNA at homologous locations in the genome. These differences in sequence can result from mutations involving a single nucleotide or deletions or insertions of variable numbers of contiguous nucleotides. Each of these variants presumably occurred in a single ancestor in the distant past. Most new mutations are extinguished through random genetic drift and never become established in the population at any significant frequency. When the gene frequency of a mutation becomes established at more than 1% to
2%, it is often given the appellation of allele. If there are two polymorphic positions within a gene, each of which has two alleles, a given individual will have up to four definable alleles. These are inherited as two parental haplotypes, each of which carries one allele from each of the two loci. Extensive population studies permit sophisticated maximumlikelihood estimates of haplotype frequencies within the population. The ability to deduce haplotypes provides a much higher degree of specificity to the analysis of genetic polymorphism, because the haplotype more accurately defines a larger inherited region of DNA. (Answer: B—An allele)
For more information, see Milford EL, Carpenter CB: 6 Immunology/Allergy: VII Immunogenetics of Disease. ACP Medicine Online (www.acpmedicine.com). Dale DC, Federman DD, Eds. WebMD Inc., New York, March 2003
Immunologic Tolerance and Autoimmunity
11. A 24-year-old black woman comes to your office complaining of bilateral hand pain, a painful mouth, and a rash on her face that is particularly bothersome when she is exposed to the sun. She has had these symptoms for 6 weeks. Her examination is remarkable for patchy alopecia and multiple mouth ulcers; the musculoskeletal examination is normal. The patient tests positive for both ANA and anti–doublestranded DNA. You make a diagnosis of systemic lupus erythematous, a disease in which autoimmunity is known to play a central role.
Which of the following is NOT a possible mechanism of tolerance?
A. Clonal deletion in the thymus
B. Failure of T cells bearing low-affinity receptors to recognize antigens in the periphery
C. Sequestration of an antigen from the immune system as a result of anatomic barriers
D. Acquisition of anergy after ligation of the T cell receptor complex in the absence of costimulation
E. T cells in the thymus with high affinity for a self-antigen undergo positive selection
Key Concept/Objective: To know the mechanisms of tolerance
Immature lymphocytes are more susceptible to induction of tolerance. Tolerance can be induced in immature lymphocytes either centrally (thymus for T cells, bone marrow for B cells) or in the periphery. If a T cell has a high affinity for a self-antigen in the thymus, it can undergo negative selection with activation-induced death (apoptosis). Positive selection in the thymus occurs when T cells bearing receptors with a moderate affinity for selfantigens receive survival and maturation signals and are exported to the periphery. Normally, these cells do not cause autoimmune phenomena because of peripheral tolerance. The most common mechanism of peripheral tolerance is the failure of T cells bearing low-affinity receptors to recognize an antigen. T cells bearing receptors with high affinity for an antigen can remain in an inactivated state if that antigen is sequestered from the immune effector cells. Apoptosis is also a mechanism of peripheral tolerance. A third mechanism of peripheral tolerance involves the acquisition of anergy after ligation with the T cell receptor complex. The most extensively characterized mechanism of anergy induction occurs when the T cell receptor is ligated in the absence of costimulation. Another mechanism of tolerance is T cell-mediated suppression, in which regulatory T cells actively inhibit an immune response to an antigen. (Answer: E—T cells in the thymus with high affinity for a self-antigen undergo positive selection)
12. You are asked to see a 34-year-old pregnant woman in the emergency department who is experiencing shortness of breath. She has pulmonary edema, and an echocardiogram shows mitral stenosis. She is from South America. When asked, she says that many years ago, she had an illness with rash, fever, and joint pain that kept her in bed for a few weeks. On the basis of this history, you make a presumptive diagnosis of rheumatic mitral stenosis.
Which of the following constitutes the best immunologic causative mechanism of rheumatic fever?
A. Direct bacterial infection of the heart
B. Antistreptocococcal antibodies cross-reacting with myocardial antigens
C. Toxins released by group A Streptococcus that cause valvular damage
D. Pathogenic autoantibodies directed against the endocardium of heart valves
Key Concept/Objective: To understand the mechanism of molecular mimicry
In rare cases, the normal immune response to a specific microbial peptide can trigger immunity to a related self-peptide, a phenomenon known as molecular mimicry. This mechanism has been described in rheumatic heart disease and Lyme disease. In the case of rheumatic heart disease, antistreptococcal antibodies cross-react with myocardial antigens. The specific peptides have not been identified. Pathogenic autoantibodies have been clearly associated with myasthenia gravis, pemphigus, and a number of endocrinopathies but not rheumatic fever. (Answer: B—Antistreptocococcal antibodies cross-reacting with myocardial antigens)
For more information, see Anderson P: 6 Immunology/Allergy: IX Immunologic Tolerance and Autoimmunity. ACP Medicine Online (www.acpmedicine.com). Dale DC, Federman DD, Eds. WebMD Inc., New York, November 2002
Allergic Response
13. A 35-year-old woman with a history of asthma and atopic dermatitis presents to your office for followup. She was recently hospitalized for community-acquired pneumonia complicated by an acute exacerbation of her asthma.
Which of the following statements most accurately describes the T cell response to allergenic peptides in an atopic patient?
A. In the TH2 response, T cells form interleukin-4 (IL-4), IL-5, and IL-13, thereby directing the production of allergen-specific antibodies
B. In the TH1 response, T cells produce interferon gamma (IFN-?), thereby inducing T cell differentiation
C. In the THO response, T cells produce IL-12 and IL-18, thereby causing differentiation from THO cells to TH1 cells
D. In the TH response, naive helper T cells differentiate into mature T
lymphocytes, producing IgG1 and IgG4 antibodies
Key Concept/Objective: To recognize T cell response in an atopic host
The pathophysiologic response to allergenic peptides such as bacterial DNA sequences differs in a normal person from an atopic patient. Bacterial DNA sequences have immunostimulatory regions containing deoxycytidine-phosphate-deoxyguanosine (CpG) repeats. CpG repeats are recognized as foreign by pattern recognition receptors called Toll-like receptor-9 (TLR-9) on antigen-presenting cells. These CpG repeats stimulate macrophages and dendritic cells to secrete inflammatory cytokines, including IL-12 and IL-18. These cytokines then induce T cells and natural-killer (NK) cells to produce IFN-?, a cytokine known to promote nonallergic, protective responses. This pattern of response by helper T cells is termed a TH1 response, because it is associated with the differentiation of naive T helper (TH0) lymphocytes into mature TH1 lymphocytes. Similarly, the T helper cells of persons without atopy respond to presentation of potentially allergenic peptides by producing IFN-and directing the production of allergen-specific IgG1 and IgG4 antibodies. In contrast, T helper cells of atopic persons respond to processed aeroallergens by forming IL-4, IL-5, and IL-13 and by directing the production of allergen-specific IgE antibodies. This type of T helper cell response is termed a TH2 response. IL-4 and IL-13 share a number of functions, which are mediated through the IL-4Ra/IL-13Ra heterodimer. However, only IL-4 is able to induce the differentiation of TH0 cells to TH2 cells and to antagonize the differentiation of TH0 cells to TH1 cells, resulting in IgE-mediated allergic inflammation. In contrast, both IL-12 and IFN-induce the differentiation to TH1 cells; TH2 cell differentiation is inhibited by IFN-?. Differentiation to TH1 cells results in cell-mediated immunity and inflammation. Therefore, the differentiation of TH0 cells to either TH1 cells or TH2 cells appears to be the crucial event that determines which type of immune response will follow. (Answer: A—In the TH2 response, T cells form interleukin-4 [IL-4], IL-5, and IL-13, thereby directing the production of allergen-specific antibodies)
14. A 28-year-old graduate student with a history of chronic allergic rhinitis and asthma presents to your clinic. His symptoms, which are continuous, have been somewhat refractory to the therapies you have tried thus far. He recently ran across a proposed new drug therapy for asthma while reading a scientific journal. The name of this drug is omalizumab, and he asks you to explain how it works.
Which of the following responses is the most accurate answer to this patient’s question?
A. Omalizumab is a monoclonal antibody that is directed against the tumor necrosis factor (TNF) receptor; it inhibits the action of TNF
B. Omalizumab is a monoclonal antibody directed against the Fce portion of IgE; it inhibits activation of mast cells
C. Omalizumab is a monoclonal antibody directed against the IL-5 receptor; it inhibits eosinophil development
D. Omalizumab is a cyclic polypeptide immunosuppressant that suppresses inflammation
Key Concept/Objective: To understand the mechanism of action of omalizumab, a promising new therapeutic agent directed against allergic response
Clearly, treatment that interferes with IgE activation of mast cells and basophils may be beneficial. Omalizumab, a recombinant, humanized monoclonal antibody directed against the Fce portion of IgE, has recently been developed. Important features of this antiIgE molecule are (1) it does not bind IgE already attached to FceRI and, therefore, does not cause anaphylaxis; (2) it does not activate complement; and (3) it has a much longer halflife than IgE. In phase III trials, omalizumab was administered by subcutaneous injections given every 2 or 4 weeks to patients with allergic rhinitis or with allergic asthma of varying severity. All studies showed dramatic reductions in free IgE levels that were dependent on omalizumab dose as well as baseline IgE levels. The posttreatment level of free IgE directly correlated with reduced symptom scores, reduced use of rescue medication, and improved quality of life. For asthma, significant reductions in asthma exacerbations, in hospitalizations for asthma, and in the dose of inhaled or oral steroids were also found. As levels of serum IgE decreased, so did surface expression of FcåRI on basophils. (Answer: B— Omalizumab is a monoclonal antibody directed against the Fce portion of IgE; it inhibits activation of mast cells)
15. An 18-year-old woman is brought to the emergency department after a bee sting. She is flushed and in mild respiratory distress. She is afebrile. Her heart rate is 110 beats/min; her blood pressure is 80/40 mm Hg; and her respiratory rate is 28 breaths/min. As you prepare to initiate supportive therapy and empirical treatment for anaphylaxis, the nurse, who has drawn blood, asks what tests you would like to order.
Which of the following serum markers, if elevated, most consistently suggests anaphylaxis as the cause of hypotension?
A. Histamine
B. Chymase
C. Cathepsin G
D. Tryptase
Key Concept/Objective: To know a serum marker that identifies anaphylaxis as a cause of hypotension
Peak plasma levels of histamine occur 5 minutes after insect-sting-induced anaphylaxis begins and decline to baseline within 20 minutes. Because they are relatively transient, these histamine elevations in plasma are difficult to utilize for the clinical determination of anaphylaxis as a cause of hypotension. However, tryptase diffuses into, and is removed from, the circulation more slowly than histamine. Tryptase levels peak in the circulation
15 minutes to 2 hours after mast cell degranulation and decline with a half-life of about 2 hours. Peak levels during insect-sting–induced anaphylaxis correlate closely to the drop in mean arterial blood pressure, which is an important measure of clinical severity. For that reason, serum or plasma tryptase levels have recently been recognized as a clinically useful marker for the diagnosis of systemic anaphylaxis. (Answer: D—Tryptase)
16. A 42-year-old woman presents to your clinic complaining of continuing allergic rhinitis. A biopsy of her nasal mucosa would almost certainly reveal eosinophils. There are several mechanisms that lead to the preferential accumulation of eosinophils, rather than neutrophils, at sites of allergic inflammation.
Of the following mediators and receptors, which is specifically involved with eosinophil chemotaxis?
A. Leukotriene C4 (LTC4)
B. CCR3 chemokine receptor
C. Very late antigen–4 (VLA-4)
D. All of the above
Key Concept/Objective: To understand the different receptors and mediators involved in the preferential accumulation of eosinophils as compared with neutrophils
Receptors for complement (C3a and C5a); the lipid mediators platelet-activating factor (PAF), LTC4, and LTB4; and numerous cytokines and chemokines bind to and activate eosinophils. Chemokines of the C-C family play an important chemotactic role for eosinophils. Chemokines of this family have the same receptors. A particular C-C chemokine receptor, CCR3, is found abundantly on eosinophils but not on neutrophils. CCR3 binds at least four chemokines that play crucial roles in the homing of eosinophils to epithelial tissues and that activate eosinophils to release mediators. Another mechanism, which leads to preferential accumulation of eosinophils rather than neutrophils at sites of allergic inflammation, relates to differences in expression of surface adhesion molecules. Eosinophils and neutrophils share several selectins and integrins that initiate rolling of circulating cells along the endothelium, as well as the subsequent firm adhesion, diapedesis, and transmigration of these cells through the vessel wall. However, eosinophils—but not neutrophils—express an integrin, VLA-4, whose ligand on endothelial cells (VCAM-1) is upregulated by IL-4 and IL-13, cytokines that are present during TH2 responses. (Answer: D—All of the above)
For more information, see Daffern PJ, Schwartz LB: 6 Immunology/Allergy: X Allergic Response. ACP Medicine Online (www.acpmedicine.com). Dale DC, Federman DD, Eds. WebMD Inc., New York, February 2003
Diagnostic and Therapeutic Principles in Allergy
17. A 28-year-old man presents to your clinic for evaluation of allergies. He has a long history consistent with allergic rhinoconjunctivitis but also experiences urticarial lesions when he eats certain types of food. He also occasionally has back pain from a recent sports injury. His medications include loratadine and low-dose corticosteroids, which were prescribed by his primary care doctor, as well as ibuprofen and a daily baby aspirin. You decide to perform skin testing on the patient.
Which of the following interventions should you recommend before performing epicutaneous testing
A. The patient should discontinue all medications 1 week before testing
B. The patient should discontinue loratadine and steroids 3 days before testing
C. The patient should discontinue loratadine 1 week before testing
D. The patient should discontinue loratadine, steroids, and ibuprofen 1 week before testing
Key Concept/Objective: To understand the use and preparation of skin tests
Of the two most common tests for allergy, skin testing and serologic testing, the former is the more rapid and sensitive. The premise for allergy testing is the interaction of an allergen with specific IgE that is either mast cell-bound or basophil-bound. To elicit a positive reaction, degranulation of mast cells or basophils must occur and histamine must be released. Therefore, medications that inhibit histamine release and activity must be discontinued before testing. These medications mainly include antihistamines; however, other medications, such as tricyclic antidepressants, may have some antihistaminic activity as well. Most antihistamines need to be discontinued 1 week before testing; however, diphenhydramine and chlorpheniramine can be discontinued 3 days before testing. Medications such as corticosteroids do not inhibit the immediate-phase response of antihistamines and therefore can be continued. Aspirin and ibuprofen have no effect on degranulation and histamine release. (Answer: C—The patient should discontinue loratadine 1 week before testing)
18. A 35-year-old man comes to your office with symptoms of nasal congestion and itchy eyes and throat.
He has been experiencing such symptoms for several years. Symptoms are present throughout the year, and he is able to enjoy outdoor activities without worsening of the symptoms. He owns a cat, which does not sleep in the same room with him. You order allergy skin testing and receive a report indicating a positive response to dust mites and cat dander.
Which of the following therapeutic interventions is the most effective for this patient’s symptoms?
A. Antihistamines
B. Removal of the allergen from the patient’s environment
C. Leukotriene receptor antagonists
D. Cromolyn sodium
Key Concept/Objective: To understand the importance of environmental control of atopic disease
Despite the advances in medications and pharmacologic therapy for allergic illnesses, the most effective therapeutic intervention is still removal of the offending agent or allergen from the patient’s environment. This includes appropriate linens for mattresses and pillows, adequate cleaning, and lowering the ambient humidity in the house to minimize mold spores. Pets should be removed from the house or kept out of the room at all times. Patients sensitive to pollen should try to minimize the amount of time spent outdoors during those times of the year when the specific pollen is prevalent. (Answer: B—Removal of the allergen from the patient’s environment)
For more information, see Grayson MH, Korenblat P: 6 Immunology/Allergy: XI Diagnostic and Therapeutic Principles in Allergy. ACP Medicine Online (www.acpmedicine.com). Dale DC, Federman DD, Eds. WebMD Inc., New York, September 2002
Allergic Rhinitis, Conjunctivitis, and Sinusitis
19. A 20-year-old woman comes to your office in early spring with complaints of nasal congestion, runny nose, and paroxysms of sneezing. She has been experiencing these symptoms for 10 days. She denies having fever, cough, myalgias, or malaise. She states that she typically experiences bouts of similar symptoms in September and October. Her medical history includes mild intermittent asthma since childhood. On examination, she has dark rings under her eyes but no sinus tenderness. The nasal mucosa appears pale and swollen, and there is clear rhinorrhea.
Which of the following statements regarding this patient’s condition is false?
A. Nasal smear is likely to show a preponderance of eosinophils
B. Her symptoms are the result of the IgE-mediated release of substances such as histamine that increase epithelial permeability
C. Treatment of the condition can result in improvement of coexisting asthma in certain patients
D. Although daily nasal steroid sprays can alleviate symptoms, they are generally not recommended because of the risk of rhinitis medicamentosa
E. Immunotherapy can be employed in patients whose symptoms persist despite the avoidance of triggers and the use of pharmacotherapy
Key Concept/Objective: To understand the diagnosis and treatment of allergic rhinitis
Allergic rhinitis is the most common atopic disorder in children and adults in the United States. The airborne allergens responsible for the condition may be seasonal (such as pollen, grass, and mold) or perennial (such as dust mites, pet dander, and insects). In genetically predisposed persons, the antigens crosslink IgE molecules that are attached to mast cells and basophils, resulting in the release of mediators such as histamine that cause increased epithelial permeability, vasodilatation, and stimulation of a parasympathetic reflex. In addition to the common nasal symptoms, patients may display dark circles under their eyes (“allergic shiners”) and a nasal crease caused by continual upward rubbing of the tip of the nose (the “allergic salute”). Nasal smear often shows a preponderance of eosinophils (in infectious rhinitis, neutrophils predominate). In patients with coexisting asthma, control of allergic rhinitis may improve asthma control. The three arms of treatment of allergic rhinitis include trigger avoidance, pharmacotherapy (with antihistamines, decongestants, and nasal steroids), and, in certain cases, immunotherapy. The daily use of inhaled corticosteroids is the most effective therapy. Their use is not generally associated with systemic side effects. Long-term use of nasal decongestants should be avoided because this can result in rhinitis medicamentosa: an overuse syndrome in which symptoms are perpetuated. (Answer: D—Although daily nasal steroid sprays can alleviate symptoms, they are generally not recommended because of the risk of rhinitis medicamentosa)
20. A 45-year-old man with a history of seasonal allergic rhinitis presents with complaints of itching, tearing, and mild burning of both eyes. He has had these symptoms for several days. He has not had any vision changes or systemic symptoms. He reports that the ocular symptoms began in association with nasal congestion and rhinorrhea, a pattern he has experienced in the past. You suspect that he has allergic conjunctivitis.
Which of the following statements regarding the diagnosis and treatment of allergic conjunctivitis is false?
A. Bilateral involvement, although not universal, helps to distinguish the condition from acute infectious conjunctivitis
B. The presence of another atopic disorder such as allergic rhinitis, asthma, or atopic dermatitis (eczema) is present in approximately three fourths of patients with ocular allergy
C. Corticosteroid eyedrops are the most effective treatment and are generally given as first-line agents
D. Patients with viral or bacterial conjunctivitis are more likely to complain of pain and to display matting of the eyelids and purulent ocular discharge
Key Concept/Objective: To understand the diagnosis and treatment of allergic conjunctivitis
Allergic conjunctivitis is the ocular counterpart of allergic rhinitis. A majority of patients with this condition (approximately 70%) have another atopic condition, such as asthma, eczema, or allergic rhinitis. Symptoms usually include bilateral itching, tearing, and burning of the eyes. Findings on examination include conjunctival injection and periocular edema and erythema. If the patient has had direct hand-to-eye contact with an allergen such as pet dander, there may be unilateral involvement. The differential diagnosis includes viral or bacterial conjunctivitis: patients with infectious conjunctivitis more often have mucopurulent discharge with matting of eyelids, deeply red conjunctivae, and less bothersome itching than patients with allergic conjunctivitis. The first-line treatment consists of over-the-counter eyedrops containing a combination of antihistamine and decongestant (e.g., antazoline and naphazoline). Other treatments include selective H1 receptor antihistamine drops and, in severe or refractory cases, ophthalmic glucocorticoid preparations. Steroid eyedrops should be given only in consultation with an ophthalmologist because long-term use of these agents is associated with an increased risk of cataracts, glaucoma, and secondary ocular infection. (Answer: C—Corticosteroid eyedrops are the most effective treatment and are generally given as first-line agents)
21. An 18-year-old man comes to clinic complaining of nasal stuffiness, left-sided maxillary tooth pain, and postnasal drip. He has had these symptoms for more than 2 months. After the first 2 weeks of symptoms, he was seen in a walk-in clinic and given a 5-day course of antibiotics, but his symptoms did not improve significantly. He has not had fever or chills but complains that he wakes up with a sore throat on most days; the throat pain tends to get better as the day goes on. On examination, he is afebrile, with mild tenderness to palpation over the left maxilla and left forehead. His posterior oropharynx is slightly erythematous, with yellowish drainage present, but there is no tonsillar exudate. Examination of the nares reveals hyperemic mucosa and mucopurulent discharge.
Which of the following statements regarding this patient’s condition is true?
A. Chronic sinusitis can be defined as sinus inflammation that persists for more than 3 weeks
B. Sinus radiographs are the procedure of choice for evaluating patients suspected of having chronic sinusitis
C. It is likely that anaerobic bacteria are the primary pathogens responsible for this patient’s condition
D. Nasal culture has sufficient sensitivity and specificity to guide further antimicrobial therapy
E. In patients with medically resistant chronic sinusitis, further workup for conditions such as cystic fibrosis, structural abnormality, or fungal infection is appropriate
Key Concept/Objective: To understand the approach to chronic sinusitis
Rhinosinusitis can be classified as acute or chronic. Acute rhinosinusitis is defined as sinusitis that persists for more than 8 weeks in adults and for more than 12 weeks in children. Chronic sinusitis is defined as sinusitis that persists from 8 to 12 weeks or as documented sinus inflammation that persists for more than 4 weeks after initiation of appropriate medical therapy. This patient has findings consistent with chronic sinusitis, which may occur after acute sinusitis if mucopus is not sufficiently evacuated. Patients often have unilateral nasal congestion and discharge, purulent postnasal secretions, fetid breath, and facial pain. Although it was previously thought that anaerobic organisms were responsible for chronic sinusitis, it has recently been shown that aerobes are likely the primary pathogens. Chronic inflammation, rather than infection, may be the most important etiologic factor in many patients. Alhough nasal culture does not adequately reflect the bacterial pathogens that may play a role in sinusitis, microscopic examination of nasal secretions may help in diagnosis; for instance, sheets of polymorphonuclear leukocytes and bacteria suggest sinusitis, whereas predominance of eosinophils suggests allergic rhinitis. The diagnostic value of plain films (which may demonstrate mucosal thickening, air-fluid levels, or opacification) is controversial; currently, limited coronal computed tomography of the paranasal sinuses is considered the radiographic test of choice. Whereas cost was once prohibitive, costs are roughly comparable between the two imaging techniques at present. CT may additionally give useful anatomic detail that radiographs cannot and can better rule out the possibility of an anatomic abnormality that has predisposed the patient to chronic obstruction of sinus drainage. Other important considerations in a patient who has failed to respond to appropriate therapy include cystic fibrosis (especially in a younger patient with recurrent or chronic sinusitis), infection with an atypical organism such as a fungus, and Wegener granulomatosis. (Answer: E—In patients with medically resistant chronic sinusitis, further workup for conditions such as cystic fibrosis, structural abnormality, or fungal infection is appropriate)
For more information, see Slavin RG: 6 Immunology/Allergy: XII Allergic Rhinitis, Conjunctivitis, and Sinusitis. ACP Medicine Online (www.acpmedicine.com). Dale DC, Federman DD, Eds. WebMD Inc., New York, January 2005
Urticaria, Angioedema, and Anaphylaxis
22. A 43-year-old woman comes to your clinic complaining of nonhealing hives. She says that she started having hives 6 weeks ago. The hives are mildly pruritic. When asked, she says that each individual hive lasts for 2 or 3 days. Physical examination reveals multiple urticarial papules that do not blanch on diascopy. You ask the patient to come back to your clinic after 3 days, and you confirm that some of the lesions are still present.
On the basis of this patient’s history and physical examination, what would be the next step in the workup?
A. Administer thyroid function tests
B. Perform an abdominal CT scan to rule out an intra-abdominal malignancy
C. Check sinus films, hepatitis serology, and stool studies for ova and parasites
D. Perform a biopsy of one of the lesions
Key Concept/Objective: To understand the indication for biopsy in cases of urticaria
Urticaria is a very common disorder, and an etiology cannot be found in the majority of cases. The patient described here has urticarial lesions, each of which persists for more than 24 hours. Generalized urticarial lesions that persist for longer than 24 hours, produce a burning sensation, or are not very pruritic may be a manifestation of vasculitis. Lesions associated with rheumatic illness usually do not blanch on diascopy and may result in ecchymosis and eventually hyperpigmentation. A biopsy should be performed on any urticaria that lasts more than 24 hours, is only mildly pruritic or nonpruritic, is associated with vesicles or bullae, or does not respond to appropriate therapy. The subtleties of the histologic variances demand interpretation by a dermatopathologist. Approximately 5% to 10% of patients with chronic urticaria have been reported to have antithyroid antibodies, but there is only anecdotal evidence that treating these patients with thyroid hormone leads to a significant improvement. Lymphomas and carcinomas may promote urticaria, but urticaria in patients with neoplasms is usually coincidental. In most cases the malignancy is known, and current evidence does not warrant routinely subjecting patients with unexplained urticaria to an exhaustive evaluation for an occult neoplasm. Urticaria has been associated with several different infections, but extensive searches for infections as the cause of urticaria are consistently unsuccessful. (Answer: D—Perform a biopsy of one of the lesions)
23. A 34-year-old man presents to your clinic complaining of a recurrent, extremely pruritic rash on his trunk and back. The rash started a few months ago. The rash comes and goes; the patient thinks it appears when he exercises or eats spicy foods. Physical examination reveals multiple 2 to 3 mm scattered papular wheals surrounded by large, erythematous flares.
Which of the following is a likely diagnosis for this patient?
A. Cholinergic urticaria
B. Pressure urticaria
C. Idiopathic urticaria
D. Aquagenic urticaria
Key Concept/Objective: To understand the different forms of urticaria
There are several forms of physical urticaria with distinct clinical presentations. Papular urticaria consists of 4 to 8 mm wheals, often grouped in clusters and especially appearing in areas of exposed skin. Papular urticaria is very pruritic; it is usually caused by insect bites. Delayed pressure urticaria results from localized, continuous pressure (4 to 6 hours). The lesions of cold urticaria develop 5 to 30 minutes after exposure to cold, and cold urticaria can be caused by wind, water, and contact. Solar urticaria is a rare idiopathic disorder in which erythema heralds a pruritic wheal that appears within 5 minutes of exposure to a specific wavelength of light and dissipates within 15 minutes to 3 hours after onset. Aquagenic urticaria appears 2 to 30 minutes after water immersion, regardless of water temperature. The lesions of cholinergic urticaria are highly distinctive: they consist of 2 to 3 mm scattered papular wheals surrounded by large, erythematous flares. These lesions are extremely pruritic; they may affect the entire body but often spare the palms, soles, and axilla. Precipitating stimuli include exercise, warm temperature, ingestion of hot or spicy foods, and possibly emotional stress. The condition often remits within several years but can last for more than 30 years. The diagnosis can be made by provocation with exercise or a hot bath. (Answer: A—Cholinergic urticaria)
24. While traveling in an airplane, a flight attendant asks you to evaluate a 44-year-old woman who has sudden onset or urticaria, flushing, pruritus, shortness of breath, nausea, and vomiting. You learn that she has a history of allergy to peanuts and that she may have eaten some without knowing it. On physical examination, the patient is alert and is in moderate respiratory distress. Her blood pressure is 90/50 mm Hg, and her heart rate 120 beats/min. She has diffuse inspiratory and expiratory wheezing, and she is experiencing diffuse urticaria.
What is the most appropriate treatment for this patient?
A. Administer oxygen and start I.V. steroids and I.V. fluids; the flight can be continued
B. Start an I.V., inject 1 mg of epinephrine I.V., and give I.V. steroids, I.V. fluids, and oxygen; the flight can be continued
C. Administer oxygen and epinephrine subcutaneously or intramuscularly, give I.V. antihistamines and I.V. fluids, start steroids, and ask the pilot to land and transport the patient to an emergency care facility
D. Give oral antihistamines and oral prednisone and continue to watch the patient for further clinical deterioration
Key Concept/Objective: To understand the appropriate treatment of anaphylaxis
Anaphylaxis is an explosive, massive activation of mast cells, with release of their inflammatory mediators to the skin, respiratory tract, and circulatory system. The classic symptoms of anaphylaxis include flushing, urticaria, angioedema, pruritus, bronchospasm, and abdominal cramping with nausea, vomiting, and diarrhea. Hypotension and shock can result from intravascular volume loss, vasodilation, and myocardial dysfunction. The essential steps in the treatment of anaphylaxis are prevention, recognition, prompt therapy, and early transport to an emergency care facility. Anaphylaxis can rarely be overtreated. Treatment must be expeditious and appropriate. Supplemental oxygen should be given, and aqueous epinephrine (1:1,000) should be administered subcutaneously or intramuscularly. The epinephrine dose is 0.2 to 0.5 mg in adults and 0.01 mg/kg in children. If the patient is in cardiopulmonary arrest, epinephrine (1:10,000) should be administered intravenously in a dose of 0.1 to 1 mg in adults and 0.001 to 0.002 mg in children. Intravenous H1 antihistamines and H2 antihistamines should be given. Once the reaction is under control, systemic corticosteroids may be administered, and the patient should be transferred to an emergency care facility. (Answer: C—Administer oxygen and epinephrine subcutaneously or intramuscularly, give I.V. antihistamines and I.V. fluids, start steroids, and ask the pilot to land and transport the patient to an emergency care facility)
For more information, see Beltrani VS: 6 Immunology/Allergy: XIII Urticaria, Angioedema, and Anaphylaxis. ACP Medicine Online (www.acpmedicine.com). Dale DC, Federman DD, Eds. WebMD Inc., New York, February 2003
Drug Allergies
25. A 50-year-old woman is admitted to the hospital with a history of subjective fever of 2 weeks’ duration.
The patient underwent mitral valve replacement surgery 5 years ago; in addition, she once experienced an allergic reaction to penicillin, which she describes as a rash that occurred a few minutes after she received a single dose of I.V. penicillin. Physical examination is remarkable for the presence of a diastolic and systolic murmur in the mitral area. Transthoracic echocardiography shows a vegetation in the mitral valve. Blood cultures show penicillin-sensitive viridans streptococci.
On the basis of this patient’s history of penicillin allergy, which of the following would be the most appropriate course of action?
A. Start a cephalosporin
B. Administer a penicillin skin test before starting antibiotics
C. Start a different ß-lactam, such as imipenem
D. Start vancomycin
Key Concept/Objective: To understand the management of penicillin allergy
Penicillin is among the most common causes of immunologic drug reactions. Most deaths from penicillin allergies occur in patients who have no history of penicillin allergy. Nonimmunologic rashes are frequently seen with ampicillin or amoxicillin in patients who have concomitant viral infections, chronic lymphocytic leukemia, or hyperuricemia, as well as in those taking allopurinol. These rashes are typically nonpruritic and are not associated with an increased risk of future intolerance of penicillin antibiotics. Most immunologic reactions to penicillins are directed against ß-lactam core determinants and are IgE dependent. Patients who have suffered IgE-mediated penicillin reactions tend to lose their sensitivity over time if penicillin is avoided. By 5 years after an immediate reaction, 50% of patients have negative skin tests. Skin testing with a major determinant preparation and penicillin G identifies 90% to 93% of patients at risk for immediate reaction to penicillin. Not everyone with a history of a reaction to penicillin should undergo skin testing, but it is important to perform such tests in patients who have a history of anaphylaxis or urticaria associated with penicillin use. Patients who have had maculopapular or morbilliform skin rashes are not at higher risk for immediate skin reaction, but skin testing may be considered because studies have demonstrated that patient histories can be unreliable. Cephalosporins and penicillin share a similar bicyclic ß-lactam structure; patients with a history of penicillin allergy are more likely than the general population to have a reaction. Carbapenems (imipenem) and carbacephems can have significant cross-reactivity with penicillin. Vancomycin would not be indicated in this patient if a skin test can be obtained; if the skin test is positive, desensitization to penicillin can be performed. (Answer: B—Administer a penicillin skin test before starting antibiotics)
26. A 33-year-old man is admitted to the hospital with fever, knee pain, and swelling. Physical examination is remarkable for fever and a swollen, red, painful right knee. Arthrocentesis shows gram-positive cocci in clusters and 150,000 white blood cells. The patient is started on vancomycin. After a few minutes, you are called to see the patient, who is complaining of flushing and back pain. His blood pressure is 90/60 mm Hg, and he has a diffuse erythematous macular rash on his trunk, abdomen, and legs.
Which of the following would be the most appropriate course of action for this patient?
A. Administer 0.3 mg of epinephrine I.M., 50 mg of diphenhydramine
I.V., and 125 mg of methylprednisolone I.V.
B. Discontinue vancomycin; await culture results and sensitivities before restarting antibiotics
C. Slow down the vancomycin infusion rate and premedicate with diphenhydramine
D. Obtain a vancomycin skin test
Key Concept/Objective: To be able to recognize the red-man syndrome
This patient has the characteristic clinical presentation of the vancomycin-related red-man syndrome, which is characterized by hypotension, flushing, erythema, pruritus, urticaria, and pain or muscle spasms of the chest and back. The syndrome is caused by non–IgE-mediated histamine release that is more likely with rapid infusion rates (> 10 mg/min). Tolerance of readministration is promoted by reduction of the infusion rate and pretreatment with H1 (but not H2) antihistamines. Anaphylaxis is treated with epinephrine, H1 and H2 blockers, and steroids. However, this patient’s clinical picture is more suggestive of the redman syndrome. The patient has septic arthritis, so antibiotics are indicated and cannot be stopped at this time. Rarer IgE-mediated reactions to vancomycin can be identified by skin tests if the clinical picture suggests an IgE-mediated mechanism. (Answer: C—Slow down the vancomycin infusion rate and premedicate with diphenhydramine)
27. A 45-year-old man with a history of diabetes and hypertension comes to the emergency department with chest pain. He is found to have a myocardial infarction with ST segment depression. After 4 days in the hospital, the patient has recurrent chest pain; ECG changes are consistent with further ischemia. His cardiologist schedules cardiac catheterization; however, the patient says that 10 years ago, when he had an abdominal CT scan, he had a bad reaction to intravenous contrast.
Which of the following would be the most appropriate approach in the management of this patient?
A. Proceed with the catheterization; premedicate with corticosteroids and antihistamines; use nonionic contrast
B. Perform a contrast media radioallergosorbent test (RAST)
C. Continue with medical management
D. Obtain a contrast media skin test
Key Concept/Objective: To understand the management of patients who are allergic to contrast media
Radiographic contrast media cause non–IgE-mediated anaphylactoid reactions that involve direct mast cell and perhaps complement activation. A previous anaphylactoid reaction to contrast at any time in a patient’s history is predictive of persistently increased risk of a repeated anaphylactoid reaction, even though the patient may have tolerated contrast without a reaction in the interim. The use of nonionic contrast media and medication pretreatment can reduce the risk of reaction. One commonly used pretreatment regimen consists of corticosteroids, antihistamines, and oral adrenergic agents. This patient has a clear indication for cardiac catheterization and should undergo the procedure after premedication. Skin tests, RAST, and test dosing are not helpful in predicting a reaction. (Answer: A—Proceed with the catheterization; premedicate with corticosteroids and antihistamines; use nonionic contrast)
28. A 34-year-old woman with AIDS is admitted to the hospital with altered mental status. During workup, she is found to test positive on a Venereal Disease Research Laboratory (VDRL) test and to have elevated levels of white cells in her cerebrospinal fluid. The patient is diagnosed with neurosyphilis. Her sister reports that 15 years ago, the patient had an allergic reaction to penicillin; she describes this reaction as involving lip swelling, hives that appeared all over the patient’s body, shortness of breath, low blood pressure, and diarrhea. These symptoms occurred 10 minutes after receiving a penicillin shot.
Which of the following would be the most appropriate course of action for this patient?
A. Premedicate with corticosteroids and antihistamines; start penicillin
B. Start ceftriaxone
C. Do not start penicillin; consider erythromycin
D. Consult an allergist for desensitization
Key Concept/Objective: To understand the indications for desensitization
This patient had a life-threatening reaction to penicillin in the past; however, she currently has an infection that is best treated with penicillin. If the probability of a drug allergy is high and drug administration is essential, one may consider desensitization, in which the drug is administered in increasing doses in small increments. Because of the risk of adverse reactions, only experienced physicians should perform desensitization. Once desensitization is achieved, the drug must be continued or desensitization will be lost; the patient would then require repeated desensitization before readministration. Pretreatment with antihistamines and corticosteroids is not reliable for preventing IgE-mediated anaphylaxis. Patients with a history of penicillin allergy are more likely than the general population to have a reaction, which can be severe. Cephalosporins and erythromycin are not appropriate treatment options for neurosyphilis. (Answer: D—Consult an allergist for desensitization)
For more information, see Dykewicz MS, Gray H: 6 Immunology/Allergy: XIV Drug Allergies. ACP Medicine Online (www.acpmedicine.com). Dale DC, Federman DD, Eds. WebMD Inc., New York, August 2003
Allergic Reactions to Hymenoptera
29. Allergic reactions to insect stings can be either local or systemic. They result primarily from the stings of insects of the Hymenoptera order, which includes bees, wasps, and imported fire ants. In the United States, at least 40 deaths occur each year as a result of insect stings.
Which of the following statements is false?
A. A person who has suffered a number of uneventful stings in the past has no risk of a significant allergic reaction to future stings
B. Although almost 20% of adults demonstrate allergic antibodies to Hymenoptera venom, only 3% of adults and 1% of children suffer from anaphylaxis as the result of being stung
C. Fatalities from systemic allergic reactions are more common in people older than 45 years
D. A person’s risk of anaphylaxis varies in accordance with reactions to previous stings and with results of venom skin tests and radioallergosorbent tests (RASTs) for specific IgE antibodies
Key Concept/Objective: To understand important epidemiologic aspects of allergic reactions to Hymenoptera stings
Insect stings, which usually cause only minor local injury to the victim, can cause both local and systemic allergic reactions. Such reactions can occur in patients of all ages and may be preceded by a number of uneventful stings. Systemic (anaphylactic) reactions to Hymenoptera stings occur in approximately 1% of children and 3% of adults. An estimated 10% of adults may experience large local reactions that consist of prolonged swelling at the site of envenomation. Fatal anaphylactic reactions can occur at any age but are more common in adults older than 45 years. Half of the persons who experience a fatal reaction has no history of allergy to insect stings. RAST can detect venom-specific IgE antibodies in the bloodstream of patients with Hymenoptera allergy, although these antibodies are also found in a large number of adults (17% to 26% of the adult population) who have no history of allergic reactions. (Answer: A—A person who has suffered a number of uneventful stings in the past has no risk of a significant allergic reaction to future stings)
30. A patient who in the past suffered from anaphylaxis after a bee sting has recently moved from New York to the southeastern United States. She is concerned about increased exposure to stinging insects in this part of the country and asks your advice.
Which one of the following statements might you include in a discussion with this patient regarding the distribution and behavior of various families of Hymenoptera?
A. Africanized honeybees (“killer bees”) are present in the southeastern United States and pose a larger threat in terms of anaphylaxis because the antigen in their venom is unique and is more potent than that found in typical honeybees and bumblebees
B. Yellow jackets are relatively docile and tend to stay away from human beings, and they thus pose little threat to this patient
C. Imported fire ants have increasingly become a problem in the southeast but do not tend to cause allergic reactions, because they cause injury only by biting, not stinging
D. Paper wasps, which often build open nests under windowsills or eaves, have the ability to sting multiple times
Key Concept/Objective: To know general aspects about the behavior of Hymenoptera to appropriately counsel a patient regarding avoidance
A basic familiarity with the families of the Hymenoptera order can help the clinician to establish the cause of an allergic reaction and to educate patients regarding avoidance. Many insects are more abundant in warmer climates, such as those in the southeastern United States; if this patient spends a significant amount of time outdoors, she may be at increased risk of exposure to stinging insects. The three most important families of Hymenoptera in terms of allergic reactions are the bees (including honeybees and bumblebees), the vespids (including yellow jackets, hornets, and wasps), and imported fire ants. Honeybees are relatively docile and usually do not sting unless provoked. Often, exposure occurs as a result of gardening or stepping on a bee with a bare foot. Africanized honeybees (“killer bees”) are present in the southern United States; they have a tendency to swarm with little provocation and to sting in large numbers. Their venom is identical to that of the common honeybee, and an individual sting is no more potent. Unlike honeybees, vespids, such as yellow jackets and wasps, can sting multiple times. Yellow jackets scavenge food and are often found around picnics and garbage cans. They are aggressive and will sting without provocation: thus, allergic persons should be on the lookout for yellow jackets in the appropriate settings. Paper wasps are abundant in the southeastern United States and along the Gulf Coast; they build nests under overhangs. Imported fire ants have become an increasing hazard; their sting induces a unique sterile pustule that is readily recognized. (Answer: D—Paper wasps, which often build open nests under windowsills or eaves, have the ability to sting multiple times)
31. A mother and her 14-year-old son are in your office. Several months ago, the boy was stung by a wasp.
He subsequently developed severe swelling at the site of envenomation; the swelling increased over 24 hours and persisted for several days. He did not, however, develop generalized urticaria, dyspnea, dysphonia, or weakness. The mother is concerned about the possibility of his having a life-threatening reaction to stings and wants to know what to look for and what tests can be done to determine his risk.
Which of the following statements is false?
A. Involvement of the pulmonary and circulatory systems distinguishes a systemic allergic reaction from a severe localized cutaneous reaction
B. RAST must be interpreted in light of the patient’s allergic history because venom-specific IgE antibodies may be present in patients who have never demonstrated an allergic reaction to stings
C. RAST is less sensitive than skin testing, and up to 15% to 20% of patients with a documented anaphylactic reaction and positive skintest results may have undetectable levels of venom-specific IgE antibodies
D. The degree of reaction to a venom skin test (as measured by the size of the wheal and flare) closely correlates with the severity of a patient’s allergic reaction to stings
Key Concept/Objective: To be able to use clinical and laboratory information to diagnose allergic reactions to Hymenoptera stings
Allergic reactions to stings are IgE mediated and may be local or systemic. Local reactions are late-phase reactions consisting of swelling at the site of the sting: they may be massive and cause considerable pain. Systemic reactions, although sometimes localized to the skin (especially in children, who may develop only generalized urticaria), may also involve the pulmonary, circulatory, and gastrointestinal systems and are a medical emergency. Skin testing and RAST can help establish the diagnosis of allergy in a patient with a history that suggests the patient is at risk. Skin testing is more sensitive for detecting allergy (up to 20% of patients with a positive skin test and documented allergic reaction to a sting may not have detectable IgE with RAST), but the size of the wheal and flare reaction has absolutely no relation to the severity of the allergic response to a sting. RAST should not be performed as a screening test in patients without an appropriate clinical history, because adults who never develop allergic reactions may demonstrate venom-specific IgE antibodies. (Answer: D—The degree of reaction to a venom skin test [as measured by the size of the wheal and flare] closely correlates with the severity of a patient’s allergic reaction to stings)
32. A 25-year-old woman with a history of eczema presents to the emergency department 2 hours after being stung by a bee while gardening. Initially, swelling occurred at the site of the sting; this was followed by a diffuse urticarial eruption, dyspnea, wheezing, and dizziness. At the triage station, she is awake but somewhat lethargic. She is using accessory muscles to breathe. Her blood pressure is 94/32 mm Hg, and her heart rate is 112 beats/min.
Which of the following statements concerning this patient is false?
A. Epinephrine is the initial drug of choice for anaphylactic reactions and may be lifesaving
B. If the patient demonstrates initial improvement after treatment, it is safe to discharge her home after observing her for 2 to 4 hours
C. Corticosteroids such as hydrocortisone are appropriate to administer, although their ability to prevent late-phase reactions is debated
D. Before discharge, the patient should be instructed on the use of selfadministered epinephrine
Key Concept/Objective: To understand the acute treatment of anaphylaxis
Anaphylactic reactions to insect stings must be recognized promptly and treated urgently; failure to do so can result in patient mortality. Patients with evidence of laryngeal edema, bronchospasm, or hypotension should receive intravenous or intramuscular epinephrine without delay because it has the potential to reverse these effects. Milder reactions can be treated with subcutaneous epinephrine. It should be noted that patients taking beta blockers may be resistant to the effects of epinephrine in this setting. Other supportive measures include continuous pulse oximetry, administration of intravenous fluids, and frequent monitoring of vital signs. Additional pharmacologic adjuncts include H1 and H2 receptor antagonists, such as diphenhydramine and ranitidine; pressors, such as dopamine; and corticosteroids. There is conflicting evidence on the ability of steroids to prevent late-phase reactions, but their relatively low risk-to-benefit ratio warrants their use in most cases. In some cases, anaphylaxis is prolonged or recurrent for 6 to 24 hours and may require intensive medical care. Patients with moderate to severe systemic allergic reactions should be admitted to the hospital for observation, even if they are initially stabilized. All patients who have suffered an anaphylactic reaction should be prescribed an epinephrine autoinjector and educated on its use. (Answer: B—If the patient demonstrates initial improvement after treatment, it is safe to discharge her home after observing her for 2 to 4 hours)
33. A 32-year-old woman whose medical history includes an anaphylactic reaction to a yellow jacket sting would like to know if there are any measures she can take to decrease her risk of anaphylaxis in the event of a future insect sting. You recommend immunotherapy.
Which of the following statements best supports your recommendation of immunotherapy for this patient?
A. Children and adults with a history of large local reactions to stings are at relatively high risk for developing anaphylaxis, and venom immunotherapy in these patients is required
B. Although standard venom immunotherapy is generally well tolerated, it is only 40% to 50% effective in completely preventing systemic allergic reactions to stings
C. In a patient who has had a single anaphylactic reaction to a sting and whose skin test is positive, immunotherapy is indicated
D. In a patient receiving immunotherapy, the skin test usually becomes negative within the first 4 to 6 months; failure to do so may indicate a lack of response to the treatment
Key Concept/Objective: To understand the indications for and typical outcomes of venom immunotherapy
Patients with anaphylactic reactions to Hymenoptera stings should be educated about the risk of future reactions and about avoiding exposure. These patients should also understand the need for an epinephrine kit, and in most cases they should be evaluated by an allergist. The indications for venom immunotherapy are a history of a systemic allergic reaction to a sting and a positive venom skin test. In patients with these indications, the risk of anaphylaxis after subsequent stings approaches 50%. On the other hand, children and adults with a history of large local reactions have only a 10% chance of developing anaphylaxis after subsequent stings; in these patients, immunotherapy is an option (which many patients choose) but is not required. Standard immunotherapy is quite effective; it completely prevents subsequent systemic allergic reactions in 85% to 98% of patients. In the initial weeks of treatment, patients may develop a systemic allergic reaction, which is usually mild. Skin-test results generally remain unchanged during the first 2 to 3 years of treatment but usually decline after 4 to 6 years. The risk of life-threatening systemic allergic reactions occurring after 5 years of immunotherapy is low. Currently, it is recommended that immunotherapy be continued for an indefinite period. (Answer: C—In a patient who has had a single anaphylactic reaction to a sting and whose skin test is positive, immunotherapy is indicated)
For more information, see Golden DBK: 6 Immunology/Allergy: XV Allergic Reactions to Hymenoptera. ACP Medicine Online (www.acpmedicine.com). Dale DC, Federman DD, Eds. WebMD Inc., New York, October 2002
Food Allergies
34. A 36-year-old man is being evaluated for diarrhea. The patient has a 3-month history of diarrhea, postprandial nausea and vomiting, and weight loss. There is no specific food that he can relate to his symptoms. A complete blood count reveals anemia and eosinophilia. His serum IgE level is increased. Small bowel biopsy reveals eosinophilic infiltration without vasculitis.
Which of the following is the most likely diagnosis for this patient?
A. Oral allergy syndrome
B. Churg-Strauss syndrome
C. Eosinophilic gastroenteropathy
D. Immediate gastrointestinal hypersensitivity
Key Concept/Objective: To be able to recognize allergic eosinophilic gastroenteropathy
Allergic eosinophilic gastroenteropathy is a disorder characterized by infiltration of the gastric or intestinal walls with eosinophils; absence of vasculitis; and, frequently, peripheral blood eosinophilia. The symptoms include postprandial nausea and vomiting, abdominal pain, diarrhea, and, occasionally, steatorrhea. Young infants have failure to thrive, and adults have weight loss. There appears to be a subset of patients with allergic eosinophilic gastroenteritis who have symptoms secondary to food. These patients generally have the mucosal form of this disease, with IgE-staining cells in jejunal tissue, elevated IgE in duodenal fluids, atopic disease, elevated serum IgE concentrations, positive prick skin tests to a variety of foods and inhalants, peripheral blood eosinophilia, iron deficiency anemia, and hypoalbuminemia. The diagnosis of eosinophilic gastroenteropathy is based on an appropriate history and a GI biopsy demonstrating a characteristic eosinophilic infiltration. The oral allergy syndrome is a form of contact urticaria that is confined almost exclusively to the oropharynx and rarely involves other target organs. Patients with immediate GI hypersensitivity present with GI symptoms after the ingestion of a specific food. Churg-Strauss syndrome is a form of small-vessel vasculitis; patients present with asthma, sinusitis, and eosinophilia. It can have GI manifestations as well. (Answer: C—Eosinophilic gastroenteropathy)
35. A 3-year-old boy is brought to your office by his mother, who relates that her son was diagnosed as having peanut hypersensitivity 1 year ago. He developed urticaria and nasal congestion after ingestion of peanuts. Since then, he has had two more episodes of hypersensitivity, with similar symptoms. His mother asks about treatment.
Which of the following is the most appropriate treatment for this patient?
A. Long-term use of antihistamines
B. Immunotherapy
C. Elimination diet
D. Ketotifen
Key Concept/Objective: To understand the management of food allergy
The only proven therapy for food allergy is the strict elimination of that food from the patient’s diet. Elimination diets should be supervised, because they may lead to malnutrition or eating disorders, especially if they involve the elimination of a large number of foods or are utilized for extended periods of time. Studies have shown that symptomatic food sensitivity generally is lost over time, except for sensitivity to peanuts, tree nuts, and seafood. Symptomatic food sensitivity is usually very specific; patients rarely react to more than one member of a botanical family or animal species. Consequently, clinicians should confirm that patients are not unnecessarily limiting their diet for fear of allergic reactions. Except in the case of patients who are at risk for life-threatening reactions to minuscule amounts of peanuts, immunotherapy is not useful in food allergies. The importance of prompt administration of epinephrine when symptoms of systemic reactions to foods develop cannot be overemphasized. (Answer: C—Elimination diet)
36. A 30-year-old woman presents with shortness of breath, angioedema, urticaria, and hypotension after eating shellfish. She is successfully treated with epinephrine, intravenous fluids, and antihistamines. She has a history of asthma and hypertension. She takes lisinopril and inhaled beclomethasone. Radioallergosorbent testing reveals the presence of shellfish-specific IgE.
Which of the following statements regarding this patient’s condition is the most accurate?
A. She had a type III hypersensitivity reaction
B. This allergy is likely to disappear in a few years
C. She should avoid other highly allergenic foods, such as peanuts and tree nuts, as well as shellfish
D. She is at high risk for developing a more severe anaphylactic reaction in the future if she ingests shellfish
Key Concept/Objective: To know the risk factors for severe anaphylactic reactions
Risk factors for severe anaphylaxis include the following: (1) a history of a previous anaphylactic reaction; (2) a history of asthma, especially if the asthma is poorly controlled; (3) allergy to peanuts, nuts, fish, or shellfish; (4) current treatment with beta blockers or angiotensin-converting enzyme (ACE) inhibitors; and, possibly, (5) female sex. This patient had a type I, or IgE-mediated, hypersensitivity reaction. A type III reaction is antigen-antibody complex mediated. Allergies to foods such as tree nuts, fish, and seafood are generally not outgrown, regardless of the age at which they develop. Persons with these allergies are likely to retain their allergic sensitivity throughout their lifetime. (Answer: D—She is at high risk for developing a more severe anaphylactic reaction in the future if she ingests shellfish)
For more information, see Burks AW: 6 Immunology/Allergy: XVI Food Allergies. ACP Medicine Online (www.acpmedicine.com). Dale DC, Federman DD, Eds. WebMD Inc., New York, September 2003