Micro & Immunology · single question
A patient with lupus erythematosus presents with an allergic reaction. Which type of hypersensitivity is the mechanism in systemic lupus erythematosus (SLE)?
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Correct answer: B. Type III — immune complex
SLE is a Type III hypersensitivity (immune complex–mediated). Antigen-antibody complexes (particularly anti-dsDNA antibodies) are deposited in tissues (glomeruli, skin, joints, vessels), activating complement and causing inflammatory damage. This is also called 'serum sickness–type' hypersensitivity. Type I is IgE-mediated (anaphylaxis, allergies); Type II is cytotoxic (blood transfusion reactions, Graves' disease); Type IV is cell-mediated (contact dermatitis, PPD reaction).
- A. ❌ Type I hypersensitivity is IgE-mediated, causing immediate allergic reactions (anaphylaxis, hay fever) — not SLE.
- B. ✅ CORRECT – SLE is a Type III (immune complex) hypersensitivity; immune complexes deposit in tissues and activate complement.
- C. ❌ Type II hypersensitivity involves cytotoxic antibodies against cell surface antigens (hemolytic anemia, Goodpasture syndrome) — not SLE.
- D. ❌ Type IV is cell-mediated (T-lymphocyte) hypersensitivity (contact dermatitis, tuberculin test reaction) — not SLE.
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