The Arthus reaction is a localized immune complex-mediated phenomenon. Which complement-derived mediator is MOST directly responsible for the neutrophil infiltration seen in this reaction?

• A C3b (opsonin)
• B C1q (pattern recognition)
• C C4b2a (C3 convertase)
• D C5a (anaphylatoxin) ✓

Explanation

In the Arthus reaction (Type III hypersensitivity), locally formed antigen-antibody complexes activate complement. C5a is a potent chemoattractant that recruits neutrophils to the site of immune complex deposition; C5a also activates mast cell degranulation. C3b acts as an opsonin to facilitate phagocytosis. C1q initiates the classical pathway. C4b2a is the C3 convertase of the classical pathway but is not a direct mediator of neutrophil recruitment.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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