A micro complement fixation assay was devised to measure the type-specificity of anti-M antibody. Unabsorbed sera were from rabbits hyperimmunized with heat-killed streptococci and from humans with naturally occurring antibody or immunized with purified M protein vaccines. These sera fixed complement only in the presence of homologous M proteins (serotypes 1, 3, 6, 12, and 14). The complement f...
