Host immune response · USMLE Step 1

Complement activation via the classical pathway requires which event?

  1. MBL binding to mannose
  2. Spontaneous C3 hydrolysis
  3. Antigen–antibody complexes
  4. C3b binding to pathogen surfaces
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Correct answer: Antigen–antibody complexes

The classical pathway is triggered by IgG or IgM bound to antigens. This initiates complement cascade activation.

Difficulty: Medium Question 5 of 20

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