<prompt> True about protein A of staph aureus:Causes opsonizationBinds to Fc portion of IgGStimulate phagocytosisT-cell mitogen  <response>: Ans. is b i.e., Binds to Fc part of IgGRef: Ananthanarayan, 9the, p. 197, 198 Protein A is a cell wall component of S aureus strains and is a bacterial surface protein called as microbial surface components recognizing adhesive matrix molecules MSCRAMMs.Bacterial attachment to host cells is mediated by MSCRAMMs, and these are important virulence factors.Protein A of Staph aureus binds to Fc terminal of IgG IgG 1, 2 and 4 but not IgG 3 and prevents opsono- phagocytosis by PMNs. Protein A has become an important reagent in immunology and diagnostic laboratory technology; for example, protein A with attached IgG molecules directed against a specific bacterial antigen agglutinates bacteria that have that antigen conglutination. 