Homologous and heterologous protection of mice with group A streptococcal M protein vaccines.

Purified streptococcal M proteins precipitated with alum (APM) were used to immunize mice. A trivalent vaccine of serotypes 1, 3, and 12 protected mice against challenges by homologous live streptococci and also conferred protection against serotypes 6 and 14 but not against a strain of group B streptococci. Monovalent APM vaccines afforded homologous protection and restricted heterologous protection. The extent of heterologous protection was a function of serotype combinations and was also dose dependent. Rabbit antisera exhibiting strong opsonic activities were active in vitro and in passive mouse protection only for homologous serotypes. Mouse antisera did not passively transfer protection and were not bactericidal in vitro. It was concluded that homologous and heterologous active mouse protection was most likely a result of shared antigenic determinants of the various M proteins although protection of mice could not be measured as a function of circulating anti-M antibodies.