Deck 8: Immunology

Question 1

A 7-year-old boy is brought to the office due to sudden onset of facial swelling 2 hours ago.  He has had no itching or pain other than a sore throat over the last 2 days, for which he has taken acetaminophen.  The patient has had similar episodes of facial swelling that resolved spontaneously after a few days.  Temperature is 37 C (98.6 F), blood pressure is 100/78 mm Hg, pulse is 95/min, and respirations are 24/min.  Examination shows nonpitting edema of the cheeks, lips, and tongue; there is no tenderness or erythema.  Which of the following studies is most likely to be abnormal?

A)Eosinophil count
B)Serum C4 level
C)Serum C8 level
D)Serum IgA level
E)Serum IgE level

Answer 1

B

This patient's recurrent facial swelling is most likely due to hereditary angioedema, which is characterized by a deficiency or dysfunction of C1 inhibitor (previously referred to as C1 esterase inhibitor).  Poor C1 inhibitor function leads to elevated bradykinin, a peptide that causes vasodilation and increased vascular permeability, resulting in edema.
Presentation is typically in childhood or adolescence with episodes of swelling affecting the skin (eg, face, extremities) and mucosa of the gastrointestinal tract and/or larynx.  Attacks are often precipitated by minor trauma (eg, dental procedure) or emotional stress and are not associated with itching or urticaria.
Initial evaluation of hereditary angioedema is with complement testing.  Low C4 is characteristic because, in the absence of C1 inhibitor, unregulated activation of C1 leads to excess activated C1 and, in turn, unchecked cleavage of C4.  Diagnosis is confirmed by a decrease in functional C1 inhibitor level.
(Choices A and E)  Elevated eosinophils and IgE are associated with allergic conditions.  In contrast to bradykinin-mediated hereditary angioedema, allergic angioedema (eg, anaphylaxis) is due to histamine release from activated mast cells and presents with pruritis and urticaria in addition to swelling.
(Choice C)  C8 is involved in the formation of the membrane attack complex, which, when deficient, results in increased susceptibility to Neisseria infections.  Deficiency of terminal complement components (C5, C6, C7, C8, C9) does not occur with hereditary angioedema because the upstream complement fragments (C2b, C4b) are rapidly inactivated in the plasma.
(Choice D)  Selective IgA deficiency increases risk for anaphylaxis, which can cause angioedema.  However, this risk is only with transfusion of blood products and would present with other organ system involvement (eg, bronchospasm, hypotension, urticaria).  IgA deficiency is also associated with certain autoimmune conditions (eg, celiac disease, systemic lupus erythematosus), but none of these would present with isolated facial swelling.
Educational objective:
Hereditary angioedema is characterized by recurrent episodes of cutaneous and/or mucosal swelling due to C1 inhibitor deficiency.  C4 levels are low due to uninhibited cleavage of C4 by excess activated C1.

Question 2

A 24-year-old nurse comes to the office for his annual wellness visit that includes tuberculosis screening.  The patient has no chronic medical conditions and does not have recent fever, cough, or other health changes.  He receives an intradermal injection of tuberculin on the inner surface of his forearm.  Two days later, he has a distinct area of induration 20 mm across at the injection site.  Which of the following interactions is essential to the development of this patient's skin reaction?

A)CD14 on epidermal macrophages with bacterial lipopolysaccharide
B)CD16 on natural killer cells with IgG bound to infected cells
C)CD18 on neutrophils with ICAM-1 on endothelial cells
D)CD28 on T lymphocytes with CD80 on epidermal dendritic cells
E)CTLA4 on T lymphocytes with CD80 on epidermal dendritic cells

Answer 2

D
Tuberculin skin testing (TST) introduces purified proteins from Mycobacterium tuberculosis into the dermis.  Because M tuberculosis is primarily countered by the cell-mediated immune response (CMIR), previously infected patients have primed, antigen-specific CD4 T lymphocytes that rapidly replicate and mature in response to tuberculin antigen re-exposure.
T-lymphocyte activation is a 2-step process:
Activated CD4 T lymphocytes release inflammatory cytokines (eg, IL-1, IL-6, TNF alpha) that stimulate/recruit other immune cells and increase vascular permeability, forming an indurated wheal of inflammation following TST exposure.  Tuberculin reactions appear 24-72 hours after antigen exposure due to delays between initial antigen processing by APCs, T-cell activation, and amplification of the cellular response.
(Choice A)  CD14 is a pathogen-associated molecular pattern receptor on macrophages that recognizes lipopolysaccharides and rapidly activates the innate immune response; it does not participate in TST.
(Choice B)  CD16 is a receptor on natural killer cells that binds to the FC portion of IgG attached to foreign antigens on infected cells.  Binding triggers lysis of the infected cell via antibody-dependent cellular cytotoxicity (part of the CMIR).  Antibodies do not play a significant role in TST.
(Choice C)  CD18 on circulating neutrophils binds to ICAM-1 on the endothelium, allowing neutrophils to extravasate into tissue.  Neutrophils are not a major part of TST reactions.
(Choice E)  CTLA4 is an immune checkpoint expressed by regulatory and activated T cells.  It mutes the CMIR by competing with the T-cell costimulatory ligand CD28 for binding CD80/86 (ie, B7) on dendritic cells (APCs).  Because CTLA4 binds with greater affinity than CD28 to CD80/86, it slows the activation of T cells in areas with active inflammation.
Educational objective:
Tuberculin skin testing triggers a type IV delayed-hypersensitivity reaction in patients with previous infection due to the presence of primed, antigen-specific CD4 T lymphocytes.  These lymphocytes recognize tuberculin proteins displayed on antigen-presenting cells (APCs) and become activated following a costimulatory interaction between CD28 on the T cell and CD80/86 on the APC.

Question 3

A 5-year-old child is brought to the emergency department by his parents for right arm pain.  The patient reports that he was playing hide and seek outside and felt a sharp pain on his arm while hiding in some thick bushes.  His parents suspect that something had stung him.  Physical examination shows an edematous and erythematous plaque with mild central pallor.  A residual stinger, located central to the lesion, is readily extracted.  The physical examination is otherwise not significant.  Which of the following substances is most likely directly responsible for the skin findings observed in this patient?

A)C3b
B)IL-2
C)Histamine
D)Lysozyme
E)TNF-α

Answer 3

C
This child is experiencing a local allergic reaction (type I hypersensitivity) to an insect sting.  The cutaneous findings are consistent with a wheal-and-flare reaction, an erythematous papule or plaque often with central pallor (wheal) and peripheral erythema (flare).
During initial allergen exposure, a patient predisposed to an allergic response will undergo antibody class switching from IgM to IgE antibodies specific for the allergen.  IgE produced by B lymphocytes and plasma cells then binds to high-affinity IgE Fc receptors on basophils and mast cells.  Re-exposure to the allergen results in cross-linking of bound IgE antibodies with subsequent degranulation and release of inflammatory mediators (eg, histamine, proteases [tryptase], leukotrienes, prostaglandins).  Localized vasodilation and increased vascular permeability result in the characteristic wheal-and-flare lesions.  In severe cases, widespread release of these agents can also cause systemic vasodilation, bronchoconstriction, and massive fluid shifts, leading to anaphylactic shock and potentially death.
(Choice A)  C3b, the larger subunit produced by cleavage of complement component 3, binds to pathogens and enhances phagocytosis.  The C3b component of immune complexes formed by type III hypersensitivity reactions can also bind to CR1 receptors on erythrocytes, facilitating their clearance in the liver and spleen.
(Choice B)  IL-2 is a cytokine produced by T_H1 lymphocytes that increases proliferation and activity of helper, cytotoxic, and regulatory T cells as well as NK cells.  T_H1 cells are responsible for inducing macrophage and cytotoxic T lymphocyte-mediated (type IV) inflammatory reactions.  In contrast, IL-4 is responsible for driving the production of T_H2 cells, which promote antibody-mediated (humoral) immunity and facilitate type I hypersensitivity.
(Choice D)  Lysozyme is an antimicrobial enzyme found in specific granules of neutrophils and bodily secretions (tears, mucus).  Lysozyme functions by hydrolyzing bonds within the peptidoglycan cell walls of bacterial organisms.  It is an important component of innate immunity, not hypersensitivity reactions.
(Choice E)  TNF-α is a proinflammatory cytokine produced by macrophages and T cells that induces and maintains granuloma formation (important for host defense against tuberculosis).  It also plays a pathogenic role in inflammatory conditions such as rheumatoid arthritis, psoriasis, and inflammatory bowel disease.  TNF-α may be elevated in type IV (delayed type) hypersensitivity, but not type I.
Educational objective:
Wheal-and-flare lesions usually result from allergic (type I hypersensitivity) reactions.  On initial exposure, an allergen (eg, insect venom) promotes antibody class switching to IgE.  Subsequent exposure promotes cross-linking of IgE on basophils and mast cells, resulting in degranulation and release of multiple vasoactive mediators, including histamine.

Question 4

A 5-year-old boy with severe, recurrent respiratory infections is undergoing evaluation.  Sputum studies reveal intracellular bacteria.  Further testing shows that the patient's T cells lack the IL-12 receptor.  Supplementation with which of the following substances would most likely improve this patient's condition?

A)Early complement components
B)GM-CSF
C)Immunoglobulins
D)Interferon-gamma
E)Interleukin-4

Question 5

A 33 year-old female is being followed by her neurologist for her multiple sclerosis.  She was initially diagnosed with relapsing remitting subtype after an episode of visual disturbance and an episode of paralysis.  In her study of autoimmune diseases she encounters the topic of lymphocyte development and comes across a question which she poses to her neurologist during a routine follow-up visit: During the process of T-lymphocyte maturation, T cell receptors of many lymphocytes demonstrate a very high-affinity interaction with MHC molecules expressed on thymic medullary epithelial and dendritic cells.  What process do these lymphocytes undergo at this time?

A)Affinity maturation
B)Isotype switching
C)Negative selection
D)Positive selection
E)TCR DNA rearrangement

Question 6

A 23-year-old woman comes to the physician with migratory joint pains involving her hands and knees.  Physical examination shows bilateral tenderness in her wrists and proximal interphalangeal joints.  There is also a malar skin rash and generalized lymphadenopathy.  A urinalysis reveals proteinuria.  Further evaluation shows that the patient's lymphocytes contain a mutated and functionally defective Fas gene product.  Which of the following immunologic mechanisms is most likely impaired in this patient as a result of this molecular defect?

A)Activation-induced T lymphocyte death
B)Affinity maturation of B lymphocytes
C)Clonal anergy of T lymphocytes
D)Isotype switching of  B lymphocytes
E)T_H1 and T_H2 lymphocyte differentiation

Question 7

A 19-year-old man comes to the office due to eye pain and blurry vision in both eyes for the last several days.  He sustained an open globe injury to the right eye 3 months ago after being struck during an altercation and was treated with surgical repair and prophylactic antibiotics.  The left eye was unaffected.  At the patient's last follow-up appointment, visual acuity in the right eye had improved from 20/400 to 20/80.  He is otherwise healthy.  Temperature is 37.1 C (98.8 F).  Examination is unremarkable apart from bilateral conjunctival injection and decreased visual acuity in both eyes.  Analysis of vitreous samples from both eyes demonstrates multinucleated giant cells.  Which of the following mechanisms is most likely causing this patient's current manifestations?

A)Granulomatous response to reactivation of a latent viral infection
B)Mixed inflammatory reaction triggered by a gastrointestinal pathogen
C)Neutrophilic response to an intraocular infection
D)T-cell response to previously sequestered antigens
E)Type IV hypersensitivity reaction to an antibiotic

Question 8

A 52-year-old woman comes to the emergency department with pain and redness affecting her left leg.  The patient's symptoms began 2 days ago and have progressed to the point where she cannot walk without experiencing severe pain.  Physical examination shows a large, erythematous area with indistinct margins over her left leg.  The area feels hot and indurated and is exquisitely tender.  She is admitted to the hospital for severe left leg cellulitis and is started on intravenous cefazolin.  Several minutes after the infusion is started, she experiences shortness of breath, diffuse itching, and dizziness.  Her blood pressure is 64/38 mm Hg and heart rate is 130/min.  On examination, there is a diffuse erythematous skin rash and bilateral wheezing is heard on lung auscultation. Which of the following is most likely to be elevated in this patient's serum as a result of her medication reaction?

A)Alkaline phosphatase
B)Calcitonin
C)Collagenase
D)Myeloperoxidase
E)Tryptase

Question 9

A 56-year-old woman with a history of heart failure is admitted to the hospital for orthotopic cardiac transplantation.  The patient developed biventricular failure due to idiopathic myocarditis.  She has had persistent New York Heart Association class IV symptoms refractory to maximal medical therapy and was placed on the transplant waiting list.  An ABO-compatible cadaveric heart is available for transplant with partial human leukocyte antigen (HLA) mismatch.  Cardiac transplantation is performed and the patient's T lymphocytes quickly recognize the foreign HLA molecules of the transplant cells.  Inhibition of which of the following substances would specifically reduce the proliferation and differentiation of these T lymphocytes?

A)Bcl-2
B)Calcineurin
C)E-cadherin
D)Neurofibromin
E)p53

Question 10

A 56-year-old woman comes to the emergency department with facial swelling and difficulty breathing.  She woke up today with a "feeling of fullness" in her lips, and 2 hours later her husband said that her lips looked puffy.  There is no itching or skin rash.  The patient has had no similar symptoms before.  She has a history of gastroesophageal reflux disease and takes lansoprazole daily.  She also began taking lisinopril 2 months ago for hypertension.  The patient's blood pressure is 135/75 mm Hg.  On examination, there is moderate swelling of her lips and tongue.  Mild audible stridor without wheezing is present.  Which of the following is the most likely mechanism responsible for this patient's symptoms?

A)Bradykinin accumulation
B)Hereditary C1-esterase inhibitor deficiency
C)IgE-dependent mast cell degranulation
D)Increased renin secretion
E)Nonimmune mediated mast cell degranulation

Question 11

A 75-year-old man is hospitalized due to respiratory distress.  The patient developed fever, cough, and muscle aches 4 days prior to admission.  He is otherwise healthy and has no chronic medical conditions.  The patient has received all recommended vaccinations, including a yearly flu vaccine.  Temperature is 39 C (102.2 F), blood pressure is 110/65 mm Hg, pulse is 115/min, and respirations are 29/min.  Chest x-ray shows bilateral infiltrates.  Reverse transcriptase PCR of a specimen from a nasopharyngeal swab reveals a strain of influenza A virus that was included in the seasonal trivalent flu vaccine.  The patient lives with his 50-year-old son, who received the same vaccine but did not develop the infection.  Which of the following factors most likely increased this patient's risk of vaccine failure compared with that of his son?

A)Decreased overall quality of antibodies
B)Decreased production of naive B lymphocytes
C)Diminished levels of memory T lymphocytes
D)Increased apoptosis induced by neutrophils
E)Increased phagocytosis by macrophages

Question 12

On flow cytometric analysis of a sample of fetal thymus, a certain population of cells is identified that is positive for both CD4 and CD8 cell surface antigens.  These cells are best characterized as which of the following cells?

A)Immature cortical T lymphocytes
B)Mature cytotoxic T lymphocytes
C)Mature helper T lymphocytes
D)Antigen presenting cells
E)Natural killer (NK) cells
F)Thymic epithelial cells

Question 13

The patient's anaphylactic reaction is determined to be mediated by antigen-specific IgE antibodies attached to high-affinity receptors on the surface of mast cells and basophils.  Which of the following mechanisms is most likely to trigger vasoactive substance release by these cells?

A)Antibody-receptor covalent binding
B)Antibody-receptor dissociation
C)Receptor aggregation
D)Receptor detachment from the cell surface
E)Receptor internalization

Question 14

A 65-year-old woman is enrolled in a clinical trial to test a new medication for rheumatoid arthritis.  The patient's condition has been poorly controlled despite prolonged treatment with multiple disease-modifying antirheumatic drugs.  The new medication is a CTLA4-Ig fusion protein that prevents CD28 from binding to CD80/86 on antigen-presenting cells.  A month after treatment begins, the patient reports a significant reduction in joint pain and stiffness.  Laboratory results reveal reduced levels of C-reactive protein and IL-2.  Which of the following is the most likely underlying cause of this patient's treatment response?

A)Complement inhibition
B)Immune complex clearance
C)Negative selection
D)Peripheral tolerance
E)Sensitization

Question 15

A 28-year-old woman, gravida 2 para 2, brings her healthy 6-day-old girl to the office for her first well-baby checkup.  The infant was born full-term, with a birth weight of 4.2 kg (9.3 lb) and a length of 51 cm (20 in).  She was discharged from the nursery with no concerns.  Physical examination is normal.  The infant's blood type is A negative, whereas the mother's is B negative.  High circulating levels of anti-A antibodies are found in the mother's blood.  Hemolysis did not occur in the infant because these maternal antibodies are most likely of which class?

A)IgA
B)IgD
C)IgE
D)IgG
E)IgM

Question 16

A 57-year-old woman comes to the emergency department due to cough and hemoptysis.  The patient also reports several months of fatigue and joint pain.  Physical examination is notable for crusting of the nasal mucosa, lung crackles, and scattered palpable purpura over the lower extremities.  Chest x-ray reveals bilateral, diffuse alveolar infiltrates.  Laboratory studies show normocytic anemia, red blood cell casts and protein in the urine, and positive c-ANCA.  After a confirmatory biopsy, treatment with rituximab infusion is planned.  This medication is most likely to improve this patient's condition via which of the following mechanisms?

A)Blockade of T-cell costimulation
B)Depletion of B cells
C)Disruption of leukocyte migration
D)Inhibition of cytoplasmic kinase
E)Interruption of cytokine function

Question 17

A researcher identifies a group of malignant epithelial cells in the sigmoid colon that have decreased their surface expression of MHC class I antigen.  Which of the following immune effector cell types is most likely to kill the transformed epithelial cells?

A)Neutrophils
B)Macrophages
C)Dendritic cells
D)CD4+ T lymphocytes
E)Plasma cells
F)Natural killer cells

Question 18

A 24-year-old woman comes to the office with a pruritic rash on her arms and legs; it has been present on and off for most of her life.  Examination of the posterior left leg reveals erythematous patches and papules, as shown in the exhibit. 
A similar rash is present on the right leg and bilateral antecubital fossae.  Which of the following cytokines primarily initiated her current exacerbation?

A)IL-4 and IL-13
B)IL-8 and C3b
C)IL-12 and IFN-gamma
D)IL-17 and IL-23
E)TNF-alpha and IL-1

Question 19

A 23-year-old man comes to the physician with dysuria and increased urinary frequency.  He is an active duty member of the US military and recently returned from sub-Saharan Africa, where he had been stationed for the last year.  The patient's symptoms have persisted for several months and have failed to resolve following antibiotic treatment.  His blood eosinophil count is elevated.  Urine microscopy shows schistosome eggs.  He is started on praziquantel and experiences improvement in his symptoms.  The elevated eosinophils in this patient contribute to the host defense against schistosomiasis through which of the following mechanisms?

A)Antibody-dependent cell-mediated cytotoxicity
B)B lymphocyte chemotaxis
C)Complement activation
D)Immediate hypersensitivity
E)MHC class I antigen processing

Question 20

A 1-year-old boy is brought to the office for medical evaluation.  The patient was recently diagnosed with type 1 diabetes mellitus.  He has also had chronic diarrhea, failure to thrive, and eczematous dermatitis since early infancy.  Small bowel biopsy reveals villous atrophy and extensive lymphocytic infiltration.  Immunologic testing shows significantly increased serum immunoglobulins and decreased IL-10 and transforming growth factor-beta levels.  Genetic testing reveals a missense mutation affecting FOXP3.  Which of the following is the most likely cause of this patient's current condition?

A)Defective B-cell differentiation into plasma cells
B)Dysfunction of regulatory T cells
C)Dysfunction of T-helper cell type 17
D)Impaired immunoglobulin isotype switching
E)Impaired positive selection of thymic T cells

Question 21

An 18-year-old college student is hospitalized due to a high fever and confusion.  According to the patient's roommate, the symptoms started about 6 hours ago.  The patient was feeling well this morning except for some nausea.  She has had several episodes of pneumonia in the past and had bacterial meningitis a year ago, which was treated with ceftriaxone.  Temperature is 39.1 C (102.4 F), blood pressure is 104/70 mm Hg, and pulse is 110/min.  The patient is lethargic but is able to follow simple commands and give single-word answers with prompting.  Physical examination reveals a petechial rash on the trunk and extremities, including the palms and soles.  Neck stiffness and photophobia are also noted.  Which of the following primary immune system impairments is most likely responsible for this patient's recurrent infections?

A)Defective T-cell maturation
B)Excessive production of IgE antibodies
C)Impaired cellular chemotaxis
D)Inability to form the membrane attack complex
E)Ineffective neutrophil oxidative burst

Question 22

Once the patient recovers from his acute illness, Candida antigen injection into his skin reveals no signs of inflammation after 48 hours.  The same test performed in his mother produces 12 mm of skin induration within 48 hours.  Which of the following cells are directly involved in the effector response observed in the mother?

A)B lymphocytes and CD4 T lymphocytes
B)B lymphocytes and CD8 T lymphocytes
C)CD4 T lymphocytes and fibroblasts
D)CD4 T lymphocytes and macrophages
E)CD8 T lymphocytes and eosinophils

Question 23

A 15-month-old boy is brought to the emergency department due to fever and foot swelling.  The patient first developed swelling of the right foot and fever 4 days ago.  Today, swelling of the left foot also developed.  Medical history is significant for a perianal abscess at 9 months of age.  Imaging studies reveal osteomyelitis affecting the metatarsal bones of both feet.  Intravenous antimicrobials are administered, but the patient still has fever and bilateral foot swelling 2 weeks later.  Laboratory workup shows persistent neutrophilic leukocytosis.  Bone biopsy culture grows Staphylococcus aureus.  Evaluation for an underlying diagnosis is initiated; via use of a rhodamine derivative, the patient's peripheral blood is stimulated with phorbol myristate acetate (PMA) and compared with a control.  Results of the test are shown in the image below: Which of the following processes is most likely impaired in this patient?

A)Chemotaxis
B)Complement production
C)Opsonization
D)Phagocytic metabolism
E)T-lymphocyte function

Question 24

A 55-year-old man with end-stage hepatitis C virus infection undergoes orthotopic liver transplantation from a deceased donor.  The patient has no perioperative complications and is discharged from the hospital on appropriate immunosuppressant medications.  One week after the surgery, he develops nausea, vomiting, abdominal pain, and bloody diarrhea.  Physical examination shows a painful maculopapular rash over his neck, back, and extremities that extends to the palms and soles.  Endoscopic evaluation reveals multiple ulcerations of the intestinal mucosa.  Which of the following is the most likely cause of this patient's current condition?

A)Graft B cell sensitization against host MHC antigens
B)Graft T cell sensitization against host MHC antigens
C)Host B cell sensitization against graft MHC antigens
D)Host T cell sensitization against graft MHC antigens
E)Preformed antibodies against graft ABO antigens

Question 25

A 10-year-old boy is brought to the emergency department by his parents due to increasing lethargy and high fever for the past 12 hours.  The boy was well last night but was sluggish this morning.  Over the day, his activity level and responsiveness diminished.  The patient was treated for Neisseria meningitidis bacteremia 2 years ago.  He has received all routine vaccinations and is developing normally.  Temperature is 39.6 C (103.3 F).  On examination, the patient appears ill and is poorly responsive.  He is tachycardic, but heart sounds are otherwise unremarkable.  Lungs are clear to auscultation.  Numerous purple bruise-like markings and petechiae are noted over his extremities, which have diminished capillary refill.  Blood samples are drawn for total complement (CH50) and alternative complement (AH50) measurement.  Which of the following sets of results is most likely to be found in this patient?

Question 26

An 8-year-old boy is brought to the pediatrician with fever, runny nose, and malaise.  After examining the child, the pediatrician determines that he has a viral infection and does not require any specific treatment.  The mother asks why an antibiotic is not necessary, and the physician explains the differences between bacterial and viral infections.  The immune system is composed of both cellular and humoral components, which are able to mount an effective response against many types of viral and bacterial infections.  A section of a normal lymph node is shown in the image below. The structures indicated by the arrows are most likely to contain cells undergoing which of the following processes?

A)Isotype switching
B)Negative selection
C)Tolerance development
D)VDJ recombination
E)VJ recombination

Question 27

A 28-year-old woman is treated with high-dose prednisone for severe lupus nephritis.  Several hours after therapy is initiated, she becomes very agitated and delusional.  Blood pressure is 130/70 mm Hg and heart rate is 110/min.  A basic metabolic profile, complete blood cell (CBC) count, and urinalysis are obtained.  The CBC differential is expected to show an increase in which of the following as a result of this patient's therapy?

A)Basophils
B)Eosinophils
C)Lymphocytes
D)Monocytes
E)Neutrophils

Question 28

An 18-month-old, partially vaccinated boy is brought to the office for a routine well-child examination.  His parents have elected a delayed schedule for vaccine administration based on personal preferences.  Today, the patient is scheduled to receive the Haemophilus influenzae serotype b (Hib) conjugate vaccine.  The parents are given detailed information about the vaccine, but the mother asks, "Why is 'tetanus toxoid conjugate' listed on the package insert?"  She adds that her son already received the diphtheria-tetanus-acellular pertussis (DTaP) vaccine.  The parents request an explanation for the reason the Hib vaccine contains both the capsular polysaccharide of Hib as well as the conjugated tetanus toxoid.  Which of the following best describes the purpose of Hib vaccine conjugation?

A)Decreases adverse vaccine reactions
B)Elicits T cell-dependent immune response
C)Eliminates the need for booster doses
D)Induces immunity against nontypeable H influenzae
E)Induces immunity against the conjugated toxoid

Question 29

A 35-year-old woman comes to the office due to fever, headache, severe muscle aches, and sore throat for the last 4 days.  Physical examination shows mild pharyngeal erythema and nasal congestion.  A rapid influenza antigen test is positive.  The patient's condition improves over the next several days despite receiving only symptomatic treatment.  In response to the influenza virus, infected respiratory epithelial cells begin secreting increased quantities of interferons.  The specific interferons secreted by these cells will most likely cause which of the following changes?

A)Decreased apoptosis of infected cells
B)Decreased protein synthesis by infected cells
C)Increased class II MHC expression
D)Increased intracellular killing by macrophages
E)Increased neutrophil recruitment

Question 30

A 2-year-old boy is brought to the emergency department due to 4 days of worsening cough and fevers.  This evening, the patient developed increasingly rapid breathing.  He has a history of 2 prior episodes of cervical lymphadenitis due to Staphylococcus aureus.  Temperature is 39 C (102.2 F).  Blood pressure is 100/72 mm Hg, pulse is 130/min, and respirations are 35/min.  Prominent intercostal and supraclavicular retractions are present.  There are diffuse crackles bilaterally, with decreased breath sounds at the lung bases.  Heart sounds are normal.  The patient is intubated.  Laboratory results are as follows: Bronchioalveolar lavage fluid tests positive for Aspergillus fumigatus.  Serum immunoglobulin levels are normal.  Which of the following is the most likely underlying cause of this patient's presentation?

A)Decreased macrophage degranulation
B)Disrupted macrophage phagocytosis
C)Dysfunctional neutrophil trafficking
D)Impaired neutrophilic respiratory burst
E)Reduced neutrophilic phagocytosis

Question 31

A 34-year-old woman comes to the physician for a follow-up visit.  She was diagnosed with rheumatoid arthritis 3 months ago and started on methotrexate therapy.  Despite treatment, she continues to have several hours of morning stiffness daily and frequently awakens at night due to joint pain.  Physical examination shows swelling and tenderness in the joints of her hands and wrists.  Etanercept is subsequently added to her treatment regimen.  This medication is best characterized as which of the following?

A)Cell surface receptor antibody
B)Chimeric monoclonal antibody
C)Humanized monoclonal antibody
D)Small-molecule receptor inhibitor
E)Soluble receptor decoy protein

Question 32

A 63-year-old man comes to the physician after noticing a reddish tinge to his urine for the last couple of days.  During evaluation of his hematuria, an abdominal CT scan reveals a left-sided renal mass.  Further workup also shows multiple pulmonary and bone nodules.  CT-guided biopsy of a peripherally located lung nodule demonstrates renal cell carcinoma.  High-dose interleukin-2 (IL-2) is started, and 4 weeks later there is a significant reduction in his tumor burden.  Which of the following mechanisms was most likely responsible for regression of his malignancy?

A)Anti-angiogenic effect of IL-2
B)Direct cytotoxic effect of IL-2 on the tumor cells
C)Enhanced activity of natural killer cells
D)IL-2-induced apoptosis of tumor cells
E)Increased expression of MHC Class 1 on tumor cells

Question 33

A 2-year-old boy is brought to the emergency department due to wheezing and difficulty breathing.  The patient had been trick-or-treating with his parents and ate several packs of candy containing peanuts.  After he receives an intramuscular epinephrine injection, his symptoms resolve.  At a follow up appointment, an allergy specialist places droplets of various allergens on the patient's skin and punctures the epidermis at each site.  After 15 minutes, the skin at the site with peanut extract is erythematous with a raised, itchy bump that improves by the time the family leaves the office.  Four hours later, the parents notice a hard, red swelling at the puncture site.  Which of the following is most likely involved in this secondary reaction?

A)Cell lysis following IgG autoantibody binding
B)Complement activation by immune complexes
C)Epithelial damage by major basic protein
D)IgE-mediated histamine release from mast cells
E)Interferon gamma release from CD4⁺ T cells

Question 34

A 6-year-old boy is being evaluated in the office due to a history of recurrent infections and failure to thrive.  He has been hospitalized for pneumococcal pneumonia twice and has had 5 episodes of otitis media.  The patient also has a history of prolonged diarrhea caused by Giardia intestinalis.  Physical examination shows a lack of tonsillar tissue, as well as minimally palpable cervical, axillary, and inguinal lymph nodes.  Further evaluation shows that the patient has defective signaling between activated CD4 T cells and B cells.  Which of the following laboratory findings are most likely to be found in this patient?

Question 35

A 9-year-old girl is brought to the office due to persistent nasal drainage.  Over the past 2 weeks, the patient has had increasing nasal congestion and drainage.  The discharge was initially clear but has become dark and foul smelling over the past few days.  The patient has a history of multiple skin abscesses that developed when she was an infant, but they typically do not cause discomfort.  She has also had atopic dermatitis since infancy.  Temperature is 37.1 C (98.8 F).  On examination, the patient is interactive and talkative.  Thick nasal discharge appears from both nares.  Cardiopulmonary examination is normal.  There are several diffuse areas of dry, excoriated skin along the trunk and upper extremities.  Results of a complete blood count are as follows: Which of the following patterns of immunoglobulin production is most likely to be seen in this patient?

Question 36

A 34-year-old electric company worker comes to the physician with a skin rash on his right leg.  He has not eaten any new foods or changed detergents, soaps, or lotions.  On further questioning, the patient recalls that he recently worked on a repair job in an unmaintained, wooded area.  He had atopic dermatitis as a child but no other significant illnesses.  On physical examination, he appears uncomfortable and is constantly scratching his leg.  His lungs are clear bilaterally and his heart sounds are normal.  Examination of his right leg shows the findings in the image below. Which of the following cells is most responsible for causing the tissue damage seen in this patient?

A)Basophils
B)Eosinophils
C)Mast cells
D)Neutrophils
E)Plasma cells
F)T lymphocytes

Question 37

A 10-month-old boy is brought to the office due to recurrent sinopulmonary infections for the last several months.  The infections were caused by encapsulated bacteria, and the patient was also recently hospitalized due to Pneumocystis jiroveci pneumonia.  He was born at full term after an uneventful pregnancy.  Family history is significant for a maternal uncle's early childhood death due to severe infection.  Genetic testing of the patient reveals missense mutation of the CD40 ligand gene.  Interaction between which of the following immune components is most likely impaired in this patient?

A)B cells and complement proteins
B)B cells and foreign antigens
C)Neutrophils and vascular endothelial cells
D)Phagocytes and antigen-bound antibodies
E)T cells and antigen-presenting cells

Question 38

A 3-year-old boy experiences recurrent sinusitis and an episode of severe pneumonia.  As part of his evaluation, Candida extract is injected intradermally.  Forty-eight hours later, he returns to the clinic with a firm nodule measuring 16 mm in diameter where the extract was injected.  Which of the following cell types is most likely responsible for the reaction observed in this patient?

A)B lymphocytes
B)Eosinophils
C)Mast cells
D)Neutrophils
E)T lymphocytes

Question 39

A 13-month-old boy is admitted to the hospital due to diarrhea and dehydration.  Over the past week, the patient has developed severe, watery diarrhea and has had poor oral intake.  Medical history includes multiple episodes of bronchiolitis and, at age 8 months, an intensive care unit admission due to pneumococcal pneumonia requiring a brief period of mechanical intubation and chest tube placement.  The parents say that he has been growing poorly over the past 6 months despite feeding well and supplemention with high-calorie formulas.  On examination, the patient appears lethargic with sunken eyes and poor skin turgor, as well as moderate tachycardia and tachypnea.  As part of the laboratory evaluation, flow cytometry of in vitro-stimulated CD4⁺ T cells reveals a near absence of CD40 ligand.  Which of the following additional findings is most likely associated with this patient's condition?

A)Absent thymic tissue
B)Giant granules within neutrophils
C)Hypoplastic bone marrow
D)Lack of secondary germinal centers
E)Small-volume platelets

Question 40

A 6-month-old boy is brought to the clinic by his mother and grandmother for a routine well-child visit.  The child was born full-term and has no medical problems.  He recently learned to sit with support and is starting to eat pureed foods.  Vital signs and physical examination are normal.  As part of the routine pediatric immunization schedule, the pneumococcal conjugate vaccine is ordered.  The patient's grandmother says that she recently received the pneumococcal polysaccharide vaccine.  Which of the following statements is true regarding the difference between the pneumococcal conjugate and polysaccharide vaccines?

A)The conjugate vaccine causes less local site reactions than the polysaccharide vaccine
B)The conjugate vaccine induces a more robust immune response through B and T cell activation
C)The conjugate vaccine is inactivated while the polysaccharide vaccine is live attenuated
D)The conjugate vaccine protects against meningitis but the polysaccharide vaccine does not
E)The conjugate vaccine protects against more pneumococcal strains than the polysaccharide vaccine

Question 41

The acidification of lysosomes within antigen presenting cells is prevented in an experimental setting.  The affected cells show impaired interaction with T lymphocytes upon antigen exposure.  The observed effect most likely results from a low cell surface expression of which of the following molecules?

A)Cytokine receptors
B)Integrins
C)MHC class I
D)MHC class II
E)T cell receptor

Question 42

A 3-year-old girl is brought to the office after developing fever and a sore throat.  The patient recently entered day care, and similar symptoms have been reported in several of the other children.  Physical examination shows exudative pharyngitis and enlarged anterior cervical lymph nodes.  A rapid antigen detection test confirms the diagnosis of streptococcal throat infection.  Her condition resolves with antibiotic therapy.  Several weeks later, she is re-exposed to Streptococcus pyogenes.  The bacteria penetrating beyond the surface epithelium are immediately coated with preformed IgG antibodies.  Which of the following substances acts in the most similar manner to IgG antibodies to facilitate phagocytosis?

A)5-Hydroxyicosatetraenoic acid
B)Complement C3b
C)Complement C5a
D)Immunoglobulin M
E)Leukotriene B4
F)L-selectin

Question 43

An 8-year-old male is brought to his pediatrician's office by his mother.  The child has had a runny nose, sore throat, cough, and low-grade fever for the past 24 hours.  The patient's mother recalls that several of the child's friends have been ill recently with similar symptoms.  The mother asks whether the child will need antibiotics for his condition.  His pediatrician recommends symptomatic therapy and feels that his illness is most likely of viral etiology.  Cytotoxic CD8+ lymphocytes are able to kill virus-infected nasal epithelial cells once sensitized.  Cytotoxic CD8+ lymphocyte receptors recognize foreign proteins on the epithelial cell surface.  Foreign proteins are presented on the epithelial cell surface by MHC molecules.  These MHC molecules comprise which of the following components?

A)MHC class I heavy chain only
B)MHC class I heavy chain and β₂-microglobulin
C)MHC class I heavy chain and IgG
D)MHC class II alpha-chain and beta-chain
E)MHC class II alpha-chain only

Question 44

A 13-month-old boy is brought to the emergency department due to cough and increased work of breathing.  The patient's parents immigrated to the United States when he was 6 months old.  He has a history of recurrent otitis media, pneumonia, and thrush as well as chronic diarrhea and failure to thrive.  On physical examination, he is tachypneic and has perioral cyanosis.  A chest radiograph shows bilateral interstitial opacities.  The patient is admitted to the hospital and undergoes bronchoscopy.  Analysis of the bronchoalveolar lavage fluid reveals Pneumocystis jirovecii. Which of the following is the most likely underlying diagnosis?

A)Agammaglobulinemia
B)Chronic granulomatous disease
C)Cystic fibrosis
D)Primary ciliary dyskinesia
E)Severe combined immune deficiency
F)Terminal complement deficiency

Question 45

A 68-year-old man comes to the office for a follow-up appointment.  He has a history of advanced melanoma that is unresectable and resistant to adjuvant regimens.  The patient recently began receiving monoclonal antibody infusions for advanced melanoma.  The monoclonal antibodies block a specific cell surface receptor found on T lymphocytes.  As a result, T cells capable of recognizing tumor antigens have improved ability to destroy cancer cells.  Which of the following cell surface receptors is most likely blocked by the treatment?

A)CCR5
B)CD4
C)CD19
D)CD28
E)PD-1

Question 46

A 37-year-old man comes to the emergency department because of increasing pain and tenderness in his right forearm.  During a bar brawl 6 days earlier, he sustained a 4-cm laceration through the skin and subcutaneous tissue of his forearm.  Treatment at the time of injury included cleaning and dressing the wound.  Physical examination shows erythema surrounding the wound site and expression of yellow pus when pressure is applied adjacent to the wound.  Which of the following molecules is most likely responsible for causing accumulation of pus over this patient's wound?

A)Bradykinin
B)C3a
C)IL-3
D)IL-8
E)IL-10
F)Leukotriene C₄

Question 47

An 18-month-old boy is evaluated for recurrent infections.  He has been hospitalized 3 times with pneumonia since age 3 months.  He has also had multiple skin infections requiring treatment with antibacterial and antifungal agents.  During his last episode of pneumonia, he developed a large pleural effusion, which was drained.  The pleural fluid revealed numerous neutrophils containing a large number of intact gram-positive cocci.  The microorganisms responsible for this patient's recurrent infections most likely produce which of the following virulence factors?

A)Catalase
B)Coagulase
C)Lecithinase
D)Lipopolysaccharide
E)Polysaccharide capsule

Question 48

A research scientist is comparing surface antigens X and Y that come from 2 different viruses.  He obtains antibodies against antigen X from an animal previously exposed to the virus expressing this antigen.  These antibodies are then attached to assay plates.  Next, a fixed quantity of radiolabeled X antigen is added to the plates.  Unlabeled Y antigens are then added in increasing concentrations to each plate, and the plates are washed to remove unbound antigens.  Radioactivity is plotted as a function of Y antigen concentration, as shown in the graph below. Which of the following best describes the results of this experiment?

A)Antigen X and antigen Y have no epitopes in common
B)Antigen X and antigen Y have the same epitopes
C)Antigen Y shares most of the epitopes of antigen X
D)Antigen Y shares some of the epitopes of antigen X

Question 49

A 57-year-old man underwent lung transplantation for severe emphysema 2 years ago.  Over the last 6 months, he has had increasing exertional dyspnea and dry cough.  The patient has adhered to his medical regimen.  He does not smoke and has no exposure to secondhand smoke.  Physical examination shows scattered bilateral rales and end-expiratory squeaks.  Cardiac auscultation reveals no murmurs or additional sounds.  Spirometry demonstrates markedly decreased FEV1 compared with findings 6 months prior, although the FVC remains largely unchanged.  Chronic lung transplant rejection is suspected, and bronchoscopy with transbronchial biopsy is planned.  Histopathology is most likely to show injury predominantly involving which of the following structures?

A)Alveolar walls
B)Large airways
C)Pleural membranes
D)Small airways
E)Small blood vessels

Question 50

A 2-week-old infant is brought to the emergency department due to fever, lethargy, grunting, and poor feeding.  The patient was born at full term after an uneventful pregnancy and has had no prior medical issues.  Blood samples are obtained for culture, and the patient is hospitalized for broad-spectrum antibiotic therapy.  Cultures grow Escherichia coli.  The patient's condition developed in part due to exposure to bacterial lipopolysaccharide, which stimulates NF-kB-induced transcription of inflammatory cytokines such as TNF-alpha, IL-1, and IL-6.  This bacterial component most likely interacted with the patient's immune cells via which of the following?

A)Beta-2 integrin
B)Fc receptor
C)L selectin
D)MHC class II molecule
E)Mannose-binding lectin
F)Toll-like receptor

Question 51

A 68-year-old man comes to the emergency department with a 2-day history of fever, chills, and productive cough.  His temperature is 38.9 C (102 F), blood pressure is 108/52 mm Hg, pulse is 102/min, and respirations are 26/min.  Crackles and bronchial breath sounds are heard over the right lower lung.  There is dullness to percussion over the same area.  Chest x-ray reveals right lower lobe consolidation and a right-sided pleural effusion.  The patient is started on the appropriate treatment, and a diagnostic thoracentesis is performed that shows an uncomplicated parapneumonic effusion.  When a sterile sample of the inflammatory exudate is experimentally introduced into normal human tissue, rapid neutrophil locomotion is observed.  Which of the following components of the exudate is most likely responsible for this observed effect?

A)Bradykinin
B)C4a
C)IFN-γ
D)IL-4
E)Leukotriene B₄
F)Thromboxane A₂

Question 52

A scientist is interested in the mechanisms by which leukocytes traffic to sites of inflammation and infection.  She finds that endothelial cells increase the expression of certain cell surface molecules in response to cytokines to allow for leukocyte trafficking.  She subsequently creates a knockout mouse that has a deletion in the platelet endothelial cell adhesion molecule 1 (PECAM-1) gene.  The protein product of this gene is mainly localized to specific areas on the endothelial cells.  Absent expression of this gene will most likely affect which of the following neutrophil functions?

A)Crawling
B)Margination
C)Rolling
D)Tight adhesion
E)Transmigration

Question 53

The immune response in a healthy 12-year-old boy is observed after a recurrent bacterial infection.  It is characterized by a rapid increase in pathogen-specific immunoglobulin levels.  The immunoglobulins bound to the bacteria also attach to phagocytic cells (eg, macrophages, neutrophils) to enhance phagocytosis.  Which of the following immunoglobulin regions is most likely involved in interacting with these phagocytic cells?

A)Constant region of the heavy chain
B)Constant region of the light chain
C)Hinge region
D)Variable region of the heavy chain
E)Variable region of the light chain

Question 54

A 5-year-old girl is brought to the office for evaluation of a persistent cough.  The patient has had a productive cough daily for the past month.  History includes recurrent episodes of otitis media despite bilateral ear tube placement, numerous lower respiratory tract infections, and occasional ulcerative skin lesions.  Laboratory evaluation shows normal levels of total B and T cells and serum immunoglobulin.  Genetic testing reveals a mutation in the TAP1 gene, which encodes a protein involved in the transport of cytosolic molecules into the endoplasmic reticulum.  Which of the following processes is most likely to be impaired by this mutation?

A)B cell differentiation into plasma cells
B)Cytotoxic T cell activation by MHC class I molecules
C)Destruction of phagocytized organisms
D)MHC class II molecule expression on B cells
E)Migration and extravasation of neutrophils

Question 55

Preventive disease specialists working in a developing country are investigating vaccination options to limit the spread of poliomyelitis.  As part of the study, 2 patients are vaccinated against poliomyelitis.  One patient receives an intramuscular inactivated vaccine and the other patient receives a live attenuated oral vaccine.  One month after vaccination, the levels of which of the following poliovirus antibodies will differ the most between these 2 patients?

A)Cerebrospinal fluid IgG
B)Duodenal luminal IgA
C)Serum IgA
D)Serum IgG
E)Serum IgM

Question 56

A 4-year-old male is exposed to latex gloves during a minor surgical procedure and is subsequently found to produce anti-latex IgM antibodies.  Several months later he develops a severe allergic reaction to latex and is found to have a high level of serum anti-latex IgE antibodies.  Which of the following cytokines is most likely responsible for this anti-latex antibody isotype change?

A)IL-1
B)IL-2
C)IL-3
D)IL-4
E)IL-10
F)IL-12

Question 57

Pharmacology researchers develop a novel monoclonal antibody medication to treat the wet form of age-related macular degeneration.  The antibody binds vascular endothelial growth factor, decreasing abnormal blood vessel formation in the subretinal space.  In a clinical trial, the medication is found to improve visual function.  During the next phase of the study, researchers use only the antigen binding fragment (Fab) of the antibody instead of the whole immunoglobulin.  Which of the following is most likely to be observed with use of the antibody fragments compared to the intact immunoglobulin?

A)Decreased renal excretion of the drug
B)Greater tissue penetration of the drug
C)Higher receptor-mediated uptake by macrophages
D)Increased complement-dependent cytotoxicity
E)Lower affinity for the target antigen

Question 58

A 10-month-old boy is hospitalized for respiratory distress due to Pneumocystis jiroveci pneumonia.  The patient has had repeated episodes of otitis media and thrush; weight is below the 5th percentile.  Laboratory evaluation reveals normal levels of circulating B and T cells with low levels of all immunoglobulins.  Genetic testing reveals a rare autosomal recessive mutation resulting in a defect in the regulation of human leukocyte antigen gene transcription.  Flow cytometry of the patient's peripheral blood compared with a healthy control is shown in the illustration below: Which of the following processes is most likely to be impaired by this patient's mutation?

A)Development of pharyngeal pouches
B)Capability of activated CD4⁺ T cells to express CD40L
C)Maturation of pro-B cells into pre-B cells
D)Presentation of antigens processed in lysosomes
E)Transport of cytosolic proteins into the endoplasmic reticulum

Question 59

Immunoglobulins of different classes have different structures.  Some immunoglobulins have long hinge regions between the Fab and Fc regions, whereas others lack the hinge region, as shown in the image below: The hinge region provides movement flexibility to the Fab regions.  This is most likely to affect which of the following immunoglobulin properties?

A)Affinity to antigen
B)Antibody polymerization
C)Avidity to antigen
D)Effector cell interaction
E)Effector cell specificity

Question 60

Pharmacology researchers are developing a new antivenom to treat coral snakebites.  They immunize horses with snake venom, extract IgG-containing plasma, and then administer the plasma to humans who have been bitten by a coral snake.  This therapy neutralizes the venom and improves the patient's symptoms.  In order to produce venom-selective antibodies, the researchers select a single venom-specific plasma cell from the immunized horse and induce it to proliferate and produce large amounts of venom-specific IgG.  However, they find that the antibody produced by the single plasma cell is less effective at neutralizing the venom than the IgG-containing plasma.  A decrease in which of the following best explains the reduced efficacy of the immunoglobulin produced by the single plasma cell?

A)Affinity of the individual immunoglobulin
B)Avidity of the individual immunoglobulin
C)Number of antigen epitopes recognized
D)Valency of the individual immunoglobulin

Question 61

A 44-year-old man with diabetic nephropathy undergoes a renal transplant.  One week later, he develops low-grade fever, body aches, and decreased urine output.  Temperature is 37.2 C (99 F), blood pressure is 124/76 mm Hg, and pulse is 88/min.  Physical examination shows mild tenderness over the graft on palpation.  Serum creatinine is 2.2 mg/dL, an increase from 1.2 mg/dL two days ago.  Arterial and venous Doppler studies reveal adequate graft perfusion.  Graft biopsy demonstrates dense interstitial infiltration by mononuclear cells.  Which of the following is the most likely cause of this patient's current condition?

A)Graft B-cell sensitization against host MHC antigens
B)Graft T-cell sensitization against host MHC antigens
C)Host B-cell sensitization against graft MHC antigens
D)Host T-cell sensitization against graft MHC antigens
E)Preformed antibodies against graft ABO antigens

Question 62

A 24-year-old, previously healthy woman is evaluated for skin rash, joint pains, and renal failure.  She is found to have decreased C3 and C4 levels and a normal factor B level.  Which of the following most likely triggered the complement system activation in this patient?

A)Antigens binding to IgA
B)Autoactivation of C3 component
C)C1 components binding to C1 inhibitor
D)C9-lipid membrane complex formation
E)IgG-antigen complex formation

Question 63

A 57-year-old woman with autosomal dominant polycystic kidney disease develops end-stage renal disease and undergoes deceased-donor kidney transplantation.  During the operation, the surgeon notices that the graft becomes cyanotic and mottled soon after its blood vessels are connected with those of the recipient.  Blood flow to the graft ceases, and no urine is produced.  Which of the following best explains the findings observed by the surgeon?

A)Activation of recipient T lymphocytes
B)Antibody recognition of graft HLA components
C)Degranulation of recipient mast cells and basophils
D)Donor T lymphocyte-mediated vasculopathy
E)Severe renal graft atherosclerosis

Question 64

A 26-year-old man returns to the emergency department after developing a fever and skin rash.  The patient was discharged from the hospital 10 days ago after treatment for a copperhead snake bite to his left leg.  He received multiple doses of polyvalent Fab antivenom therapy and other supportive care during hospitalization.  The patient's bite site pain, swelling, and ecchymosis have resolved; however, he has developed fever, pain in multiple extremity joints, and pruritic rash over the past 2 days.  He has no chronic medical conditions.  Temperature is 38.5 C (101.3 F), blood pressure is 128/70 mm Hg, pulse is 98/min, and respirations are 17/min.  Physical examination shows a diffuse urticarial rash.  No mucous membrane lesions are present.  There is tenderness to palpation of the bilateral metacarpophalangeal joints, wrists, and ankles with no redness or swelling.  Blood cell counts, serum chemistry studies, and coagulation parameters are within normal limits.  Which of the following is the most likely underlying mechanism of this patient's current condition?

A)IgE-mediated hypersensitivity reaction to the antivenom
B)Polyclonal T-cell activation by the antivenom
C)Receptor-mediated phagocytosis of unbound antivenom
D)Snake venom-induced diffuse mast cell degranulation
E)Tissue deposition of host antibodies and antivenom complexes

Question 65

A 24-year-old man burns his hand after grasping the handle of a hot pan while preparing a meal.  Several minutes later, both the initial burn and the area around it are red without blistering.  When he presses on the burn, the tissue blanches.  Which of the following is most likely contributing to the reaction observed in this patient?

A)Gaps between endothelial cells in venules
B)Histamine release from mast cells
C)Neutrophil extravasation and degranulation
D)PDGF-mediated vascular proliferation
E)Prostaglandins produced by platelets

Question 66

Researchers are studying various cellular processes in normal and diseased states to find new anticancer drug targets.  They develop a medication that inhibits an intracellular enzyme that converts adenosine to inosine.  With drug use, accumulation of enzyme substrates in the neoplastic cells leads to DNA strand breaks and subsequent apoptosis.  Which of the following malignancies is likely to be most responsive to this medication?

A)Hairy cell leukemia
B)Malignant melanoma
C)Ovarian teratoma
D)Small cell lung cancer
E)Soft tissue sarcoma

Question 67

An autopsy is performed on an 8-month-old infant after his unexpected death.  Prior to death, the patient had a 1-month history of poor feeding and intermittent fever, which progressed to severe lethargy and coma.  The infant was adopted soon after birth, and there is limited information about his family history beyond documentation of an uncomplicated pregnancy and delivery at term gestation.  Brain biopsy reveals leptomeningeal inflammation and is positive for Enterovirus by PCR.  This patient would have been most likely to have which of the following laboratory findings?

A)Abnormal dihydrorhodamine test
B)Absent peripheral neutrophils
C)Absent tissue eosinophils
D)Decreased total hemolytic complement
E)Low circulating B lymphocyte count
F)Reduced serum IgG2 immunoglobulin levels

Question 68

A 4-month-old girl is brought to the office due to a rash on her cheeks for the past 2 weeks.  The rash has not spread, and the patient is often seen scratching her face.  There have been no changes in bath soaps and detergents; no animals or plants are in the house.  Vaccinations are up to date.  The patient is exclusively breastfed, with height and weight tracking along the 50th percentiles.  Vital signs are normal.  Skin examination is shown in the exhibit. 
The remainder of the examination is unremarkable.  Which of the following conditions is this patient at increased risk for developing?

A)Coronary artery aneurysm
B)Disabling arthritis
C)Food allergy
D)Proximal muscle weakness
E)Transient anemia

Question 69

A 3-month-old girl is brought to the emergency department due to fever, irritability, and vomiting for the past 2 days.  On examination, she is ill-looking, lethargic, and febrile.  Blood cultures grow Mycobacterium tuberculosis.  One of her brothers died from disseminated mycobacterial infection during infancy.  Impairment of which of the following protective mechanisms is most likely contributing to this patient's infection?

A)Antibody production
B)Complement production
C)Interferon signaling
D)Isotype switching
E)Leukocyte adhesion

Question 70

A 3-year-old boy is being evaluated for persistent diarrhea.  Although the patient seemed healthy at his 12-month well child visit, since then he has experienced 4 episodes of otitis media and 3 episodes of pneumococcal pneumonia.  He was at the 50th percentile for weight and height at 12 months but is now at the 25th percentile for height and 10th percentile for weight.  The patient is referred for upper gastrointestinal endoscopy, and Giardia lamblia is isolated from duodenal aspirates.  Further workup shows very low serum levels of all immunoglobulin types.  Flow cytometry of this patient's peripheral blood is most likely to show a near absence of cells bearing which of the following markers?

A)CD4
B)CD8
C)CD15
D)CD16
E)CD19

Question 71

A 12-month-old boy is evaluated for an eczematous rash.  Medical history is significant for several severe respiratory infections that required hospitalization.  Complete blood count shows white blood cells at 9,000/mm³ and platelets at 40,000/mm³.  The platelets seem abnormally small and deformed on the peripheral blood smear.  Which of the following is the most likely diagnosis?

A)Aplastic anemia
B)Ataxia telangiectasia syndrome
C)Chédiak-Higashi syndrome
D)DiGeorge syndrome
E)Hemolytic uremic syndrome
F)Wiskott-Aldrich syndrome

Question 72

A 72-year-old woman is brought to the emergency department from a nursing facility due to fever, chills, and hypotension.  The patient has a history of diabetes mellitus, ischemic stroke, and neurogenic bladder.  She has an indwelling urinary catheter.  Temperature is 38.8 C (102 F), blood pressure is 80/40 mm Hg, and pulse is 130/min.  The patient is lethargic and disoriented.  Her extremities are warm, and her breathing is rapid and shallow.  Lungs are clear on auscultation and there are no heart murmurs.  There is left costovertebral angle tenderness.  The urine in her catheter appears cloudy.  Her leukocyte count is elevated with left shift, and urinalysis shows pyuria and bacteruria.  Which of the following chemical mediators is most responsible for this patient's current condition?

A)Interleukin-3
B)Interleukin-4
C)Interleukin-10
D)Leukotriene B4
E)Transforming growth factor-beta
F)Tumor necrosis factor-alpha

Question 73

A 36-year-old woman with fistulizing perianal Crohn disease comes to the office for a follow-up appointment.  Eight weeks ago, the patient began receiving intermittent injections of infliximab, a chimeric human-mouse monoclonal antibody targeted against tumor necrosis factor-alpha.  She reports improvement in fistula discharge and discomfort but has experienced fever, diffuse joint pain, and an itchy rash 5-7 days after each of the recent treatments.  The symptoms spontaneously resolve after 2-3 days.  The patient has no other medical conditions and has no history of drug allergies.  A delayed drug reaction due to formation of antibodies against foreign drug components is suspected.  Which of the following mechanisms is most likely responsible for resolution of these drug reactions?

A)Activation of the mononuclear phagocyte system
B)Apoptosis of tissue mast cells and eosinophils
C)Clearance of intact drug molecules by kidneys
D)Endocytosis and degradation of mast cell-bound IgE
E)Regulatory T-cell-mediated cytotoxic T-cell suppression

Question 74

A 15-year-old boy develops severe cardiomyopathy following myocarditis from Coxsackie virus and is placed on the cardiac transplant list.  Two weeks following his cardiac transplantation from a matched donor, he develops dyspnea on exertion.  Extensive evaluation is undertaken including cardiac catheterization and endomyocardial biopsy to assess for acute allograft rejection.  Which of the following histologic findings is most consistent with this diagnosis?

A)Concentric coronary artery intimal thickening
B)Dense interstitial lymphocytic infiltrate
C)Patchy necrosis with granulation tissue
D)Perivascular infiltrate with abundant eosinophils
E)Scant inflammatory cells and interstitial fibrosis

Question 75

A 45-year-old man comes to clinic for routine follow-up.  He has a history of end-stage renal disease due to autosomal dominant polycystic kidney disease, and he underwent a deceased-donor kidney transplant 4 years ago.  The patient has hypertension that initially resolved following the transplant but redeveloped 6 months ago.  Review of his recent laboratory studies reveals a progressive increase in serum creatinine levels over the last few months.  Urinalysis is within normal limits.  On ultrasonography, the transplanted kidney is reduced in size.  A biopsy of the graft is most likely to show which of the following?

A)Dense mononuclear interstitial infiltration
B)Glomerular crescent formation
C)Obliterative vascular fibrosis
D)Tubular hypertrophy and intratubular casts
E)Vascular fibrinoid necrosis with thrombotic occlusion

Question 76

A 19-year-old woman comes to the office to discuss treatment options for seasonal sneezing, rhinorrhea, and nasal congestion.  She has had these symptoms for the past few springs and summers but is now willing to "try anything" to allow her to concentrate on her upcoming final exams.  The patient has no significant medical history, takes no medications, and has no drug allergies.  Vital signs are within normal limits and physical examination reveals mild bilateral pale and boggy nasal turbinates with copious clear mucus.  Fluticasone, an intranasal glucocorticoid, is prescribed.  Which of the following is the most likely mechanism of action of this drug?

A)Apoptosis of tissue eosinophils
B)Antagonism of leukotriene receptors
C)Binding and removal of circulating IgE
D)Reduced differentiation of regulatory T cells (Treg)

Question 77

A 25-year-old woman comes to the office due to arthralgias in her hands for the last several months.  The pain frequently involves her wrists and proximal finger joints bilaterally, and alternates between being worse in the wrists versus in the hands.  The patient has no other medical problems and takes no medications.  Complete blood count results are as follows: Further evaluation reveals proteinuria and red blood cell casts.  Which of the following is the most likely diagnosis?

A)Ankylosing spondylitis
B)Myelodysplastic syndrome
C)Primary myelofibrosis
D)Systemic lupus erythematosus
E)Vitamin B₁₂ deficiency

Question 78

An 11-year-old girl is brought to the office for a health maintenance visit.  She feels well and has no chronic medical conditions.  As part of routine care, the patient receives a first dose of the quadrivalent meningococcal conjugate vaccine and the 9-valent human papillomavirus vaccine.  Five minutes later, while being escorted to the waiting area, the patient appears pale and reports feeling dizzy.  She immediately loses consciousness, but a fall is prevented by the health care provider.  Blood pressure is 70/40 mm Hg and pulse is 46/min.  On physical examination, the patient has normal lung and heart sounds.  There is no rash.  Which of the following is the most likely cause of this patient's syncope?

A)Delayed-type hypersensitivity reaction to the vaccine
B)Excessive cytokine response to vaccine microbial components
C)IgE-mediated hypersensitivity reaction to vaccine allergen
D)Stress-induced cardioinhibitory and vasodepressor response
E)Systemic invasion by live attenuated microbial agents

Question 79

A 24-year-old recent Russian immigrant describes a long history of weight loss, night sweats and nagging cough.  Imaging and biopsy of his lungs reveal numerous apical granulomas with central caseous necrosis.  Surrounding the necrotic areas are large cells with abundant pale cytoplasm.  Which of the following surface markers is most specific for those cells?

A)CD4
B)CD7
C)CD8
D)CD14
E)CD20

Question 80

A 25-year-old man comes to the office due to a 1-month history of increasing abdominal girth and swollen extremities.  His BMI is 32 kg/m².  Laboratory evaluation shows decreased serum albumin and hypercholesterolemia, and urinalysis reveals heavy proteinuria and fatty casts.  A renal biopsy shows findings consistent with focal segmental glomerulosclerosis.  Despite aggressive medical management, the patient requires a kidney transplant from his younger sister, who is a 5 out of 6 HLA antigen match.  As a part of his posttransplant immunosuppressive regimen, he takes a medication that inhibits lymphocyte proliferation by directly blocking interleukin-2 signal transduction.  This mechanism best describes which of the following drugs?

A)Bortezomib
B)Mycophenolate
C)Prednisone
D)Rituximab
E)Sirolimus