Antigenicity of the M Proteins of Group A Hemolytic Streptococci

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Abstract
Summary: M proteins from four group A streptococcus serotypes have been extracted from cells with hot acid, further purified by column chromatography and analyzed serologically and chemically. The purified M proteins elicited typespecific antibodies when administered in various protocols to 95 rabbits in two or three dosages of 100 to 400 µg per intramuscular injection. These antibodies were assayed by the hemagglutination of tanned human erythrocytes sensitized with purified M proteins. Bordetella pertussis vaccine, sodium alginate, polyethylene glycol and dextran were used as adjuvants. Only the B. pertussis enhanced the M antibody response. Eighty per cent of the rabbits responded with positive titers ranging from 1:100 to over 1:25,000. An antiserum with a titer of 1:3200 passively protected mice against 800 LD50 doses of homologous live streptococci. Bactericidal tests with antisera also corroborated the effectiveness of the M protein immunization. None of the immunized rabbits exhibited any signs of anaphylactic reaction or delayed cutaneous hypersensitivity as a result of multiple inoculations of M proteins.