The complement fragment C5a is a potent neutrophil chemoattractant that also causes mast cell degranulation. Through which receptor on neutrophils does C5a mediate its chemotactic effect?
- A CR3 (CD11b/CD18), an integrin recognising C3bi
- B C5aR1 (CD88), a seven-transmembrane G-protein-coupled receptor ✓
- C C1qR, activating the classical complement cascade
- D Toll-like receptor 4 (TLR4), recognising lipopolysaccharide
Correct answer: B. C5aR1 (CD88), a seven-transmembrane G-protein-coupled receptor
Explanation
C5a exerts its chemotactic and activating effects on neutrophils, monocytes, and mast cells through C5aR1 (CD88), a Gi-protein-coupled seven-transmembrane receptor. Receptor binding activates phospholipase C, generates IP3/DAG, raises intracellular calcium, and drives cytoskeletal reorganisation and directional migration. CR3 (CD11b/CD18) is an integrin that recognises opsonin C3bi for phagocytosis; it is not the C5a receptor. TLR4 recognises LPS; C1qR is a separate receptor involved in clearance of apoptotic cells.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.