Hypersensitivity Reactions · Pathology

Serum sickness is a systemic hypersensitivity reaction that occurs after the administration of foreign proteins. What is the initiating event?

  1. Sensitization of IgE on mast cells
  2. Direct activation of T-cells by foreign MHC
  3. Formation of circulating immune complexes
  4. Binding of IgG to erythrocytes
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Correct answer: Formation of circulating immune complexes

Serum sickness is a systemic Type III hypersensitivity reaction. It occurs when large amounts of foreign antigen lead to the formation of immune complexes that exceed the body's clearance capacity, depositing in various tissues and activating complement.

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