During activation of the complement cascade in acute bacterial infection, one cleavage fragment performs two distinct roles: it degranulates mast cells to release histamine and serves as the principal chemoattractant directing neutrophils along a concentration gradient. Which fragment is this?

• A C3b
• B C3a
• C C5a ✓
• D C4b

Explanation

C5a is both an anaphylatoxin, triggering mast cell degranulation and histamine release, and the most important chemotactic factor for neutrophils among complement fragments. C3a is an anaphylatoxin but lacks significant chemotactic activity. C3b is the major opsonin coating bacteria for phagocytosis via complement receptors, and C4b participates in the classical pathway C3 convertase without either chemotactic or anaphylatoxic roles.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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