title: Type-specific inhibition of preopsonization versus immunoprecipitation by Streptococcal M proteins.
abstract: Purified M protein of group A streptococci inhibits in vitro phagocytosis of bacteria nonspecifically when it is mixed directly with the test blood. We devised a method of preopsonization inhibition that avoids direct contact between the test blood and the opsonic inhibitory agent. Each of the M proteins tested by this method inhibited opsonization and phagocytosis of only homologous-type streptococci. Titration of the M antigen in various purified preparations demonstrated a clear dissociation between titers of type-specific precipitating M antigen and type-specific opsonic inhibitory M antigen. Since opsonization reflects protective antibody, assays of M protein based on reaction with opsonic antibody should reflect more accurately the presence of the type-specific M determinant involved in protective immunity against streptococcal infections.
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000032:analysis; D001426:Bacterial Proteins / Q000302:isolation & purification*; D001428:Bacterial Vaccines; D004591:Electrophoresis, Polyacrylamide Gel; D000939:Epitopes; D009895:Opsonin Proteins; D010587:Phagocytosis; D011233:Precipitin Tests; D011817:Rabbits / Q000276:immunology; D013290:Streptococcal Infections / Q000276:immunology; D013291:Streptococcus / Q000276:immunology*
chemical_list: D000907:Antibodies, Bacterial; D001426:Bacterial Proteins; D001428:Bacterial Vaccines; D000939:Epitopes; D009895:Opsonin Proteins