Newly recognized distinctive M protein associated with certain M type 1 group A streptococci.

Immunological and epidemiological characteristics of M1T1 and M1T8 (T8, 25, Imp.19) group A streptococci isolated in Egypt have been described. Both strains possess a common M1 antigen. The M1T8 strains possess a second antigen which has the immunological and biological characteristics of M protein. The M1T1 strains do not possess this second M antigen. Absorbed rabbit antisera which are specific for this second antigen do not react with extracts of any of the known M protein serotypes. This second antigen is therefore a newly recognized M protein. The M1T1 and M1T8 strains had mutually exclusive geographical and temporal distributions. This finding may have been a consequence of the immunity which occurred after the initial occurrence of the M1T8 strain.