In experimental peritonitis, blocking a single complement fragment abolishes neutrophil influx while leaving mast cell degranulation by C3a largely intact. Which fragment was blocked?
- A C3b
- B C4a
- C C5a ✓
- D C1q
Correct answer: C. C5a
Explanation
C5a is the most important complement-derived chemoattractant for neutrophils, monocytes, eosinophils and basophils, and it also increases vascular permeability and induces expression of integrin ligands on leukocytes. C3a is a weaker anaphylatoxin with little chemotactic activity, explaining why mast cell responses persist when C5a is neutralized. C3b is an opsonin and C1q initiates the classical pathway.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.