Protein A, a surface protein of Staphylococcus aureus, contributes to immune evasion. Its specific mechanism of interfering with the host immune response is by binding to which region of the immunoglobulin molecule?
- A Fab region of IgA
- B J chain of IgM
- C Fc region of IgG ✓
- D Variable region of IgE
Correct answer: C. Fc region of IgG
Explanation
Protein A binds the Fc region of IgG, which opsonizes bacteria in a non-functional orientation (inside-out). This prevents phagocytic cells from recognizing the Fc portion of bound antibodies and also blocks complement activation via the classical pathway. It does not bind the Fab region, so antigen-binding capacity of the antibody is irrelevant to this evasion mechanism.
Reference: Murray, Rosenthal, and Pfaller Medical Microbiology, 9th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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