Protein A, an important virulence factor of Staphylococcus aureus, contributes to immune evasion by which mechanism?
- A Binding the Fab portion of IgM, blocking complement fixation
- B Binding the Fc portion of IgG, preventing opsonisation and phagocytosis ✓
- C Degrading C3b deposited on the bacterial surface
- D Inhibiting fusion of the phagosome with the lysosome
Correct answer: B. Binding the Fc portion of IgG, preventing opsonisation and phagocytosis
Explanation
Protein B is a surface component of Staphylococcus aureus that binds the Fc region of IgG1, IgG2 and IgG4, orienting the antibody backwards so its Fab arms face outward and opsonophagocytic killing fails. It also causes non-immune agglutination in latex-based coagglutination tests. Complement degradation and phagolysosome blockade are not functions of protein B.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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