Micro & Immunology · single question
A patient presents with an NSAIDs prescription that has recently started causing a reaction. The reaction involves mast cell activation. Which hypersensitivity type is this?
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Correct answer: B. Type I — IgE mediated
Type I hypersensitivity involves mast cells and IgE. However, NSAID reactions are often pseudo-allergic — they activate mast cells through a non-IgE mechanism (COX-1 inhibition diverts arachidonic acid to leukotriene production, which directly activates mast cells). On INBDE, if mast cells are mentioned with an immediate reaction, select Type I. The key differentiator: Type I = immediate, IgE-mast cell; Type IV = delayed, T-cell mediated.
- A. ❌ Type III is immune complex deposition — does not primarily involve mast cells.
- B. ✅ CORRECT – Mast cell-mediated reactions correspond to Type I hypersensitivity (immediate, IgE-mast cell pathway). NSAIDs can trigger mast cell activation directly.
- C. ❌ Type IV is cell-mediated (T-lymphocyte) delayed hypersensitivity — mast cells are not the primary effector cells.
- D. ❌ Type II is antibody-mediated cytotoxicity against cell surface antigens — does not involve mast cells.
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