Hypersensitivity Reactions · Pathology

The 'Arthus reaction' is a localized area of tissue necrosis resulting from acute immune complex vasculitis. This is a classic example of:

  1. Type I (anaphylactic) hypersensitivity
  2. Type II hypersensitivity
  3. Type III hypersensitivity
  4. Type IV hypersensitivity
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Correct answer: Type III hypersensitivity

The Arthus reaction occurs when antigens are injected into the skin of an individual with pre-existing circulating antibodies. Immune complexes form locally in vessel walls, triggering complement activation and neutrophilic infiltration, leading to fibrinoid necrosis.

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