Hypersensitivity and Autoimmunity Practice Questions
20 free Hypersensitivity and Autoimmunity practice questions for the USMLE Step 1. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
A patient develops hives, bronchospasm, and hypotension minutes after eating peanuts. Which hypersensitivity reaction is this?
- A Type I
- B Type II
- C Type III
- D Type IV
Correct answer: Type I
Type I hypersensitivity is IgE-mediated and causes immediate reactions such as anaphylaxis. Mast cell degranulation leads to rapid symptoms.
A newborn develops hemolytic disease of the newborn due to maternal anti-Rh antibodies. Which hypersensitivity mechanism is responsible?
- A IgE-mediated mast cell activation
- B Antibody-mediated cytotoxicity
- C Immune complex deposition
- D Delayed-type T-cell reaction
Correct answer: Antibody-mediated cytotoxicity
Type II hypersensitivity involves IgG-mediated cytotoxicity. Maternal IgG crosses the placenta and destroys fetal RBCs.
A patient with systemic lupus erythematosus develops glomerulonephritis due to circulating immune complexes. This reflects which hypersensitivity type?
- A Type I
- B Type II
- C Type III
- D Type IV
Correct answer: Type III
Type III hypersensitivity results from deposition of antigen-antibody complexes in tissues. This triggers complement activation and inflammation.
A patient undergoes a PPD skin test. After 48 hours, a firm erythematous induration appears. Which hypersensitivity type is this?
- A Type I
- B Type II
- C Type III
- D Type IV
Correct answer: Type IV
Type IV hypersensitivity is T-cell–mediated and delayed. The PPD test measures a memory T-cell response to tuberculosis antigens.
A patient develops hemolytic anemia after receiving penicillin. The drug binds to RBCs, forming a target for antibodies. Which mechanism is involved?
- A Type I hypersensitivity
- B Type II hypersensitivity
- C Type III hypersensitivity
- D Type IV hypersensitivity
Correct answer: Type II hypersensitivity
Penicillin acts as a hapten, triggering Type II antibody-mediated destruction of RBCs. Complement contributes to hemolysis.
A patient experiences serum sickness after receiving antivenom. What causes this reaction?
- A IgE-mediated histamine release
- B T-cell activation
- C Immune complex deposition
- D Autoantibody binding to tissues
Correct answer: Immune complex deposition
Serum sickness is a classic Type III hypersensitivity. Animal-derived antibodies form complexes that deposit in tissues.
Contact dermatitis due to poison ivy exposure is caused by which immune mechanism?
- A IgE-mediated mast cell activation
- B Antibody-mediated cell lysis
- C Immune complex deposition
- D Delayed T-cell hypersensitivity
Correct answer: Delayed T-cell hypersensitivity
Poison ivy causes a Type IV delayed hypersensitivity reaction. Sensitized T cells trigger inflammation upon re-exposure.
Graves disease involves autoantibodies that stimulate the TSH receptor. Which hypersensitivity type is this?
- A Type I
- B Type II
- C Type III
- D Type IV
Correct answer: Type II
Type II reactions can be cytotoxic or receptor-modulating. Graves disease involves stimulatory IgG binding to TSH receptors.
A patient with myasthenia gravis produces antibodies that block acetylcholine receptors. Which hypersensitivity classification fits this?
- A Type I
- B Type II
- C Type III
- D Type IV
Correct answer: Type II
Myasthenia gravis is a Type II hypersensitivity mediated by receptor-blocking antibodies. The result is impaired neuromuscular transmission.
A biopsy from a patient with granulomatous inflammation shows macrophages surrounded by activated T cells. Which hypersensitivity type is implicated?
- A Type I
- B Type II
- C Type III
- D Type IV
Correct answer: Type IV
Granulomas form due to a chronic Type IV T-cell–mediated response. This is common in TB and sarcoidosis.
A man develops a rash 10 days after starting a new antibiotic. Immune complex deposition is suspected. Which test helps confirm Type III hypersensitivity?
- A Elevated IgE levels
- B Low complement levels
- C Positive ANA titer
- D Peripheral eosinophilia
Correct answer: Low complement levels
Immune complexes trigger complement consumption, leading to low C3/C4 levels. This supports a Type III mechanism.
A patient with Hashimoto thyroiditis produces anti-thyroid peroxidase antibodies. What type of immune process underlies this?
- A IgE-mediated acute reaction
- B Antibody-mediated cytotoxicity
- C Immune complex deposition
- D T-cell-mediated delayed response
Correct answer: Antibody-mediated cytotoxicity
Hashimoto disease involves Type II hypersensitivity where antibodies target thyroid cells, leading to cell-mediated destruction.
A blood transfusion reaction involving fever, hypotension, and hemoglobinuria is caused by which mechanism?
- A IgE mast cell degranulation
- B Antibody-mediated RBC lysis
- C Immune complex deposition
- D T-cell-mediated cytotoxicity
Correct answer: Antibody-mediated RBC lysis
Acute hemolytic transfusion reactions involve Type II IgG or IgM antibodies causing complement-mediated RBC lysis.
A patient with rheumatoid arthritis has circulating rheumatoid factor. What does this factor bind?
- A IgG Fc portion
- B IgM heavy chain
- C Complement C5a
- D IL-1 receptor
Correct answer: IgG Fc portion
Rheumatoid factor is an IgM antibody targeting the Fc portion of IgG. It contributes to immune complex formation.
Patients with multiple sclerosis develop demyelination due to autoimmunity. What is the primary mechanism?
- A Type I IgE reaction
- B Type II antibody-dependent cytotoxicity
- C Type III immune complex disease
- D Type IV T-cell–mediated destruction
Correct answer: Type IV T-cell–mediated destruction
MS involves T-cell–mediated destruction of oligodendrocytes. This categorizes it as a Type IV reaction.
A patient develops hematuria following a streptococcal infection. Immune complex deposition in glomeruli is seen. What disease is most likely?
- A Goodpasture syndrome
- B Graves disease
- C Post-streptococcal glomerulonephritis
- D Pemphigus vulgaris
Correct answer: Post-streptococcal glomerulonephritis
PSGN is caused by Type III immune complex deposition after strep infection. Complement activation causes glomerular inflammation.
A patient shows blistering skin lesions in which antibodies target desmoglein. What is the mechanism?
- A Type I hypersensitivity
- B Type II hypersensitivity
- C Type III hypersensitivity
- D Type IV hypersensitivity
Correct answer: Type II hypersensitivity
Pemphigus vulgaris is mediated by Type II antibodies against desmoglein. This causes loss of keratinocyte adhesion.
A patient develops urticaria after receiving radiocontrast dye. Which mediator is primarily released during this reaction?
- A Interleukin-2
- B Histamine
- C Interferon-gamma
- D TNF-alpha
Correct answer: Histamine
Histamine is released from mast cells during IgE-mediated Type I hypersensitivity reactions. It causes vasodilation and itching.
A patient with celiac disease develops intestinal damage due to T-cell activation against gluten peptides. Which hypersensitivity type is this?
- A Type I
- B Type II
- C Type III
- D Type IV
Correct answer: Type IV
Celiac disease involves a Type IV T-cell–mediated response to gluten. Chronic inflammation leads to villous atrophy.
A patient with Goodpasture syndrome produces autoantibodies attacking basement membranes. What type of hypersensitivity reaction is involved?
- A Type I
- B Type II
- C Type III
- D Type IV
Correct answer: Type II
Goodpasture syndrome is a classic Type II reaction targeting the basement membrane. Complement activation causes lung and kidney injury.