Immuno Patho MCQS

Question 1

A 15-year-old girl develops pruritic blotchy erythema over her arms, legs, and trunk within an hour of eating seafood, followed by diarrhea. It resolves within 3 hours. Most likely immunologic abnormality?

Accepted Answer

Localized anaphylaxis — Food allergies are type I hypersensitivity. IgE bound to mast cells in skin and GI submucosa triggers degranulation upon allergen exposure, causing urticaria and diarrhea.

Question 2

A 55-year-old man has progressive renal failure and back pain. Renal biopsy shows pink amorphous material with apple-green birefringence on Congo red staining, positive for lambda light chains. Most likely underlying condition?

Accepted Answer

Multiple myeloma — Lambda light chains from abnormal plasma cells = AL amyloidosis. Back pain suggests vertebral bone involvement by multiple myeloma, the most likely plasma cell dyscrasia.

Question 3

A 22-year-old woman has 3 years of myalgias, chest pain, arthralgias, a friction rub, bilateral pleural effusions, and mild normocytic anemia. Most appropriate initial screening test?

Accepted Answer

Antinuclear antibody test — Multisystem inflammation + pleural effusions + friction rub in a young woman = likely autoimmune disease. ANA is the best initial screening test, followed by more specific antibodies.

Question 4

A male infant at 1 year has failure to thrive and recurrent bacterial pneumonias with H. influenzae and S. pneumoniae. Most likely diagnosis?

Accepted Answer

X-linked agammaglobulinemia — Recurrent bacterial infections after maternal antibodies wane in a male infant = X-linked agammaglobulinemia (Bruton). Absent B-cell function leads to no gamma globulin production.

Question 5

A 52-year-old man receives a renal allograft with HLA-DR (Class II) antigen matching. He does not develop rejection. Which immunologic abnormality has most likely been avoided?

Accepted Answer

CD4 lymphocyte activation — Class II HLA antigens (HLA-DR) are involved in activating CD4 helper T lymphocytes. Matching these antigens prevents the helper T cell response that drives rejection.

Question 6

Two brothers have recurrent pneumonia, meningitis, sinusitis, and infections with Pneumocystis and Giardia. IgG 47, IgA 5, IgM 671 mg/dL. Normal B and T cells. Most likely gene mutation?

Accepted Answer

CD40L — Very high IgM + very low IgG and IgA = hyper-IgM syndrome. CD40L mutation prevents CD40-CD40L interaction needed for isotype switching from IgM to other classes.

Question 7

A 20-year-old woman has 6 months of symmetrical proximal muscle weakness. Deltoid biopsy shows inflammatory infiltrates and focal myofiber necrosis. ANA and anti-Mi-2 are positive; Jo-1 is negative. Most likely additional finding?

Accepted Answer

Skin rash — Anti-Mi-2 positive + proximal muscle weakness + inflammatory myopathy = dermatomyositis. The violaceous heliotrope skin rash is a characteristic feature, often subtle and limited to the face.

Question 8

A hypersensitivity response is stimulated by IL-4 and IL-5 release and is accompanied by eosinophilia. This response is most likely directed against which of the following?

Accepted Answer

Liver flukes — IL-4 and IL-5 are TH2 cytokines that drive IgE production and eosinophilia. This response is characteristic of parasitic (helminth) infections such as liver flukes that invade tissues.

Question 9

A 54-year-old woman has cold-induced finger pallor and pain, mild dyspnea, BP 170/110, ANA positive at 1:256 with a nucleolar pattern, and normal creatinine. Most likely autoimmune disease?

Accepted Answer

Systemic sclerosis — Nucleolar ANA pattern + Raynaud phenomenon + hypertension + pulmonary involvement = systemic sclerosis (scleroderma). Hypertensive emergency is a feared complication.

Question 10

Twelve hours after hiking through dense foliage, a 40-year-old man develops a raised, tender reddish rash on his uncovered forearm that intensifies over 2 days then fades over 2 weeks. Most likely hypersensitivity mechanism?

Accepted Answer

Type IV hypersensitivity — Delayed onset (12 hours), progressive rash from plant contact = contact dermatitis (poison ivy). This is a classic type IV (cell-mediated, delayed-type) hypersensitivity reaction mediated by T lymphocytes.

Question 11

A 30-year-old woman has myalgias, bilateral pleural effusions, ANA 1:1024, and BUN of 30. Renal biopsy shows granular immunofluorescence staining with anti-C1q antibody. This pattern is most typically produced by which mechanism?

Accepted Answer

Antigen-antibody complexes — Granular immunofluorescence = immune complex (type III hypersensitivity) deposition. Complexes are trapped along glomerular basement membranes, as seen in SLE.

Question 12

A second-pregnancy infant boy is born with hydrops fetalis and marked icterus. Hemoglobin is 7.5 g/dL. Which immunologic mechanism best explains these findings?

Accepted Answer

Complement mediated cell destruction — Rh incompatibility → maternal anti-Rh IgG crosses the placenta → complement-mediated destruction of fetal RBCs (type II hypersensitivity) → hemolytic disease of the newborn.

Question 13

A 12-year-old girl develops chest pain, fever, migratory polyarthritis, subcutaneous nodules, and choreiform movements 3 weeks after streptococcal pharyngitis. ASO and anti-DNase B titers are elevated. Most likely immunologic mechanism?

Accepted Answer

Bypass of low-zone tolerance through cross-reactivity — Rheumatic fever follows Group A Strep infection. Streptococcal M proteins cross-react with cardiac antigens, bypassing tolerance and causing immune-mediated cardiac and joint damage.

Question 14

A 60-year-old woman has 20 years of crippling hand and foot arthritis with ulnar deviation and swan-neck deformities. Rheumatoid factor and anti-CCP are markedly elevated. Rectal biopsy shows Congo red-positive amorphous deposits. Most likely precursor protein?

Accepted Answer

Serum amyloid-associated protein — Rheumatoid arthritis → chronic inflammation → elevated SAA (serum amyloid-associated protein) → secondary (reactive, AA) amyloidosis depositing in multiple organs including the rectum.

Question 15

A 35-year-old man has malar rash, polyarthritis, cold sensitivity, lymphadenopathy, anemia, leukopenia, and elevated CK. ANA positive 1:256. Which additional serologic test is most likely to determine his underlying disease?

Accepted Answer

Anti-RNP — Malar rash + arthritis + Raynaud + elevated CK + anemia = mixed connective tissue disease (MCTD). Anti-RNP is the defining autoantibody, combining features of SLE, RA, and scleroderma.

Question 16

A 48-year-old man has 2 months of cough and fever. Transbronchial biopsy shows epithelioid macrophages, Langhans giant cells, and lymphocytes. Most likely immunologic response?

Accepted Answer

Type IV hypersensitivity — Granuloma formation with epithelioid macrophages and Langhans giant cells = classic type IV (cell-mediated) hypersensitivity. Reactivation TB is the prototypical example.

Question 17

A 9-year-old boy develops dark urine and hematuria 17 days after streptococcal pharyngitis. Renal biopsy shows granular IgG and complement deposition around glomerular capillary loops. Most likely hypersensitivity mechanism?

Accepted Answer

Type III — Granular immune complex deposition in glomeruli following strep infection = poststreptococcal glomerulonephritis, a classic type III hypersensitivity reaction. Streptococcal antigens form complexes that deposit in the kidney.

Question 18

A 40-year-old woman has progressive dysphagia and stiff, immobile fingers with no joint pain. She has lost facial wrinkles. Skin biopsy shows extensive dermal fibrosis with almost no inflammatory infiltrates. Most likely condition?

Accepted Answer

Limited systemic sclerosis — Dysphagia (esophageal dysmotility) + sclerodactyly + facial skin tightening + dermal fibrosis without inflammation = limited systemic sclerosis (CREST syndrome), the more benign scleroderma variant.

Question 19

A 28-year-old woman develops severe respiratory stridor, tachypnea, and diffuse erythematous rash within minutes of receiving intravenous penicillin. Most likely chemical mediator responsible?

Accepted Answer

Histamine — Immediate systemic anaphylaxis after penicillin = type I hypersensitivity. Histamine released from mast cell degranulation causes vasodilation, increased vascular permeability, and bronchoconstriction.

Question 20

A 42-year-old man has weight loss, small joint arthritis, recurrent bacterial respiratory infections, chronic diarrhea with Giardia, hemolytic anemia, and low IgA 70, IgG 303, IgM 64. Normal T cells, slightly reduced B cells. Most likely condition?

Accepted Answer

Common variable immunodeficiency — Low but not absent immunoglobulins + normal T cells + slightly reduced B cells + bacterial and Giardia infections in an adult = common variable immunodeficiency (CVID). B cells cannot differentiate into plasma cells.

Question 21

A 31-year-old woman has bilateral pleural and pericardial effusions. Anti-ds-DNA is 1:512. If BUN rises to 55 mg/dL, it will most likely result from which pathologic process?

Accepted Answer

Immune complex deposition — SLE causes renal failure through type III hypersensitivity with immune complex deposition in glomeruli. Anti-ds-DNA is highly specific for SLE and correlates with lupus nephritis activity.

Question 22

A 28-year-old woman undergoes allogeneic bone marrow transplant with 5/6 HLA match. Three weeks post-engraftment she develops a fine scaling skin rash over her trunk and upper extremities. Most consistent complication?

Accepted Answer

Keratinocyte apoptosis — Post-allogeneic transplant skin rash = acute graft-versus-host disease. Donor lymphocytes attack host epidermal keratinocytes causing apoptosis. Liver and GI tract are the other two main targets.

Question 23

A 22-year-old woman develops erythema over her cheeks and nose when outdoors in sunlight. IgG deposits along the skin basement membrane by immunofluorescence in involved skin only. ANA is negative. No other symptoms. Most likely diagnosis?

Accepted Answer

Discoid lupus erythematosus — Photosensitive malar rash + IgG along basement membrane in involved skin only + negative ANA + no systemic involvement = discoid lupus erythematosus (DLE), limited to the skin.

Question 24

A 37-year-old woman develops a malar rash after sun exposure. Urinalysis shows hematuria and proteinuria. Skin biopsy shows C1q immunofluorescence at the dermal-epidermal junction. Most likely additional complication?

Accepted Answer

Pericarditis — SLE with immune complex deposition (type III hypersensitivity) along basement membranes. Complexes deposit in pericardium, pleura, synovium, and glomeruli. Pericarditis is a classic SLE complication.

Question 25

An 11-month-old infant has had continuous infections since birth with Pneumocystis, Pseudomonas, CMV, and oropharyngeal candidiasis. Autopsy shows hypoplastic thymus and absent lymph node germinal centers. Most likely mechanism?

Accepted Answer

Adenosine deaminase deficiency — Both B and T cell failure + hypoplastic thymus + continuous infections from birth = SCID. ADA deficiency accounts for about half of SCID cases, causing toxic metabolite accumulation that destroys both T and B lymphocytes.

Question 26

Every spring, a young man has nasal congestion, sneezing, and watery eyes. He improves with loratadine. His symptoms are most likely produced by chemical mediator release from which cell type?

Accepted Answer

Mast cell — Seasonal allergic rhinitis (hay fever) = type I hypersensitivity. Pollen allergens cross-link IgE on mast cells → histamine release → nasal congestion, sneezing, watery eyes. Antihistamines (loratadine) block H1 receptors.

Question 27

A 28-year-old woman has 13 months of episodic dyspnea, non-productive cough, and mild fever that improve on vacation. CXR shows nodular infiltrates. Transbronchial biopsy shows extrinsic allergic alveolitis. Most likely explanation?

Accepted Answer

Parrots in her house — Symptoms that improve away from home + return upon coming back = bird fancier's disease. Organic dust from bird feathers triggers type III hypersensitivity (Arthus reaction/extrinsic allergic alveolitis).

Question 28

A 30-year-old man has weight loss, chronic diarrhea, then develops Pneumocystis pneumonia, CMV retinitis, and oral candidiasis. Most likely lab finding?

Accepted Answer

CD4 lymphocyte count of 100/microliter — Multiple opportunistic infections (Pneumocystis, CMV, Candida) = AIDS. CD4 count below 200/microliter is the threshold at which AIDS-defining opportunistic infections occur in HIV infection.

Question 29

A 40-year-old woman has 2 years of constant dry mouth and dry eyes with SS-A autoantibodies and positive ANA. What is the worst long-term complication of her underlying disease?

Accepted Answer

Monoclonal B-lymphocyte proliferation — Dry eyes + dry mouth + SS-A antibody = Sjögren syndrome. The worst long-term complication is development of non-Hodgkin lymphoma from chronic immune dysregulation and B-cell activation.

Question 30

A 3-year-old boy has had numerous bacterial infections since infancy. He has rudimentary lymph node germinal centers on biopsy. Serum IgG is 110 mg/dL. Normal WBC differential. Positive Candida skin test. Most likely immunologic disorder?

Accepted Answer

Failure of B cell maturation into plasma cells — Recurrent bacterial infections + very low IgG + rudimentary germinal centers + intact T-cell function (positive skin test) = X-linked agammaglobulinemia (Bruton). B cells fail to mature into immunoglobulin-secreting plasma cells.

Question 31

A 28-year-old man suffers a bee sting and his wife urgently searches for injectable epinephrine. Which immunologic mechanism are they trying to circumvent?

Accepted Answer

Release of preformed tryptase — Systemic anaphylaxis from bee venom = type I hypersensitivity. Mast cell degranulation releases preformed mediators including tryptase, histamine, and heparin. Epinephrine counteracts the vasodilation and bronchospasm. Tryptase is a marker for mast cell degranulation.

Question 32

A 35-year-old man has progressive spinal immobility, hip pain, loss of lumbar lordosis, and bilateral sacroiliitis with ankylosis on X-ray. ANA is negative. Most likely lab finding?

Accepted Answer

HLA B27 — Progressive spinal ankylosis + sacroiliitis + negative ANA + no other joint involvement = ankylosing spondylitis. HLA-B27 is strongly associated, though not everyone with HLA-B27 develops the disease.

Question 33

A 44-year-old man has lifelong mild chronic diarrhea and minor respiratory infections. During a blood transfusion after a car accident, he develops an anaphylactic transfusion reaction. Most likely underlying disease?

Accepted Answer

Selective IgA deficiency — Anaphylaxis during blood transfusion + lifelong mild GI and respiratory issues = selective IgA deficiency. These patients develop anti-IgA antibodies and react anaphylactically to IgA in transfused blood products.

Question 34

A 55-year-old woman has progressive dysphagia, BP 210/110, and a positive ANA with nucleolar pattern on immunofluorescence. Normal serum complement. Most likely renal biopsy finding?

Accepted Answer

Hyperplastic arteriolosclerosis — Nucleolar ANA + dysphagia + severe hypertension = diffuse systemic sclerosis. Hypertensive emergency causes hyperplastic arteriolosclerosis (onion-skinning) in small renal arteries — a feared complication of scleroderma.

Question 35

A positive tuberculin skin test shows 15 mm of firm dark red induration at 60 hours after PPD injection. Most likely type of hypersensitivity reaction?

Accepted Answer

Type IV hypersensitivity — Delayed reaction peaking at 48–72 hours + induration (not just redness) + requires prior sensitization = type IV (cell-mediated/delayed-type) hypersensitivity, mediated by memory T lymphocytes responding to mycobacterial antigens.

Question 36

A study shows a band of IgG immunofluorescence at the dermal-epidermal junction in skin biopsies. This pattern is most likely based on which pathologic mechanism?

Accepted Answer

Trapping of antigen-antibody complexes — Linear or granular IgG band at the dermal-epidermal junction = immune complex trapping along basement membranes, a type III hypersensitivity pattern seen in SLE and other autoimmune diseases.

Question 37

A renal transplant recipient one month post-op has rising creatinine. Biopsy shows graft destruction by cells recognizing class I HLA antigens. Most likely mediating cell?

Accepted Answer

CD8 lymphocyte — Class I HLA antigens are recognized by CD8 cytotoxic T lymphocytes. CD8 cells directly kill graft cells expressing foreign class I antigens — the primary mechanism of acute cellular rejection.

Question 38

HIV-infected persons have years of clinical latency despite a viral reservoir in lymphoid tissues. Which cell type is most important in maintaining this reservoir?

Accepted Answer

Macrophage — Macrophages can be infected by HIV and survive, serving as a long-lived reservoir for virus that can spread to other cells. Follicular dendritic cells also capture and present HIV in lymphoid follicles.

Question 39

A 21-year-old man with IgA 22, IgG 175, IgM 40 mg/dL has high fever and cough with yellowish sputum and bilateral patchy infiltrates. Most likely inflammatory cell type in his sputum?

Accepted Answer

Neutrophil — Acute bacterial pneumonia in a patient with hypogammaglobulinemia = neutrophilic exudate producing purulent yellowish sputum. Innate immunity (neutrophils) responds to acute bacterial infection even when antibody production is impaired.

Question 40

A 31-year-old man sustains a crush injury to his right eye. One month later he has decreased vision in both eyes with choroidal thickening and CD4 lymphocyte and macrophage infiltration of the uvea on enucleation. Most likely immunologic mechanism?

Accepted Answer

Release of sequestered antigens — Sympathetic ophthalmia: eye trauma releases previously sequestered ocular antigens → immune response attacks both eyes. These antigens were never exposed to the immune system during development so tolerance was never established.

Question 41

A neonate has tetany, a heart murmur, serum calcium of 6.3 mg/dL, and a VSD. Over the first year he develops Pneumocystis, Aspergillus, and viral upper respiratory infections. Most likely explanation?

Accepted Answer

22q- chromosome deletion — Hypocalcemia (absent parathyroids) + cardiac defects + T-cell deficiency causing fungal and viral infections = DiGeorge syndrome. Chromosome 22q11 deletion causes failure of 3rd and 4th pharyngeal pouch development → absent thymus and parathyroids.

Question 42

A 46-year-old woman has progressive muscular weakness that worsens with repetitive movement. Motor strength goes from 5/5 to 4/5 with use. CT shows an anterior mediastinal mass. ANA is negative. Most likely immunologic mechanism?

Accepted Answer

Binding of anti-receptor antibody — Fatigable weakness + anterior mediastinal mass (thymoma) = myasthenia gravis. Autoantibodies directed against acetylcholine receptors (type II hypersensitivity/anti-receptor antibody) block neuromuscular transmission.

Question 43

A 45-year-old woman has recurrent episodes of painful swelling in her hands and feet. Over 6 years, her hands become deformed and she develops subcutaneous nodules on extensor surfaces of her elbows. Most likely lab finding?

Accepted Answer

Elevated rheumatoid factor — Symmetric small joint arthritis + ulnar deviation + subcutaneous rheumatoid nodules on extensor surfaces = rheumatoid arthritis. Rheumatoid factor and anti-CCP are the characteristic serologic markers.

Question 44

A 7-year-old boy has recurrent bacterial infections since infancy, eczema, ecchymoses, and a platelet count of 44,000. His brother and paternal uncle are similarly affected. Most likely diagnosis?

Accepted Answer

Wiskott-Aldrich syndrome — Eczema + thrombocytopenia + recurrent infections + X-linked inheritance = Wiskott-Aldrich syndrome. Caused by deficiency of WASP protein involved in actin cytoskeletal functions affecting immune and platelet cell function.

Question 45

Persons with inflammatory bowel disease have ulcerating bowel lesions with a TH17 immune response extending over decades. Which cell type is mediating the tissue injury?

Accepted Answer

T lymphocytes — TH17 is a subset of helper T lymphocytes that produce IL-17, promoting neutrophil recruitment and chronic mucosal inflammation. T lymphocytes are the primary mediators in this cell-mediated (type IV) chronic inflammatory bowel response.

Question 46

A 47-year-old woman has 2 years of dry mouth, eye discomfort, and bilateral painless parotid enlargement. A year later she develops swelling, warmth, and pain in her hands. Most likely autoantibody?

Accepted Answer

SS-A — Xerophthalmia + xerostomia + parotid enlargement = Sjögren syndrome. SS-A (anti-Ro) is the characteristic autoantibody. The subsequent joint involvement suggests co-existing rheumatoid arthritis, a common overlap.

Question 47

HIV crosses the vaginal mucosa. Within the epithelium it encounters a cell without CD4 receptors that transports it to a regional lymph node. What is this transporting cell?

Accepted Answer

Dendritic cell — Langerhans cells (epithelial dendritic cells) lack CD4 receptors but capture HIV and transport it via lymphatics to regional lymph nodes, where they present it to CD4 T cells, facilitating viral spread.

Question 48

A 48-year-old man has severe pain, swelling, and tenderness in his left first metatarsophalangeal joint. Joint aspiration shows neutrophils and needle-shaped crystals. His acute response is most likely mediated through crystal-induced NOD-like receptor signaling of which of the following?

Accepted Answer

Inflammasome — Needle-shaped (sodium urate) crystals in the joint = acute gout. Crystals activate NOD-like receptors → inflammasome assembly → caspase-1 activation → cleavage of pro-IL-1β to active IL-1β → acute inflammatory arthritis.

Question 49

A 54-year-old man with chronic hepatitis C develops a hepatocyte clone with loss of growth control and poor MHC class I expression. Which cell most likely destroys this abnormal clone?

Accepted Answer

NK cell — NK cells are programmed to destroy cells with poor or absent MHC class I expression. When a neoplastic or virally infected cell downregulates MHC I, NK cells recognize and kill it — a key mechanism of tumor immune surveillance.

Immuno Patho MCQS

Questions, Answers & Explanations