Complement fragment C5a plays multiple roles in acute inflammation. Which of the following is NOT a direct action of C5a?

• A Chemotaxis of neutrophils and monocytes
• B Opsonization of bacteria for phagocytosis by neutrophils ✓
• C Mast cell degranulation causing histamine release
• D Priming of respiratory burst in neutrophils

Explanation

Opsonization is performed by C3b (and C4b), which bind to the bacterial surface and are recognized by complement receptor 1 (CR1) on phagocytes. C5a is an anaphylatoxin and potent chemotactic factor for neutrophils and monocytes, activates mast cell degranulation (increasing vascular permeability), and primes the neutrophil respiratory burst/oxidative killing. C5a does not directly opsonize bacteria — that is specifically the role of C3b in the complement cascade.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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