Protein A, a surface virulence factor of Staphylococcus aureus, mediates immune evasion by which specific mechanism?

• A Direct lysis of complement C3b on the bacterial surface
• B Binding to the Fc region of IgG, preventing opsonophagocytosis ✓
• C Cleaving secretory IgA at the mucosal surface
• D Inhibiting neutrophil chemotaxis by blocking IL-8 receptors

Explanation

Protein A binds the Fc region of IgG molecules, coating the bacterial surface with antibodies in the wrong orientation. This prevents Fc receptor-mediated phagocytosis by neutrophils and macrophages, effectively blocking opsonization. IgA protease is produced by organisms like Neisseria and Haemophilus. Complement evasion in S. aureus involves other factors like staphylococcal complement inhibitor (SCIN).

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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