Characterization of the antibody response to type 12 M protein of group A streptococcus.

Group A streptococcal M protein is defined by its ability to stimulate type-specific precipitating and protective antibodies. Type 12 M protein was prepared by the acid-heat extraction of whole cells and ammonium sulfate precipitation. Acrylamide gel electrophoresis of the resulting M protein revealed multiple protein bands. The acrylamide gel was divided into three parts and protein from each part was tested for the ability to stimulate antibodies in rabbits. Only the proximal two portions of the gel produced protective antibody as measured by the long-chain and mouse-protective tests. Protein in all sections of the gel stimulated the production of precipitating and hemagglutinating antibodies. A low level of protective antibody as measured by the indirect bactericidal test was present only in the antisera to Part 1 of the gel. The results indicate that M protein stimulates antibodies with different functions.