Heterogeneity of group A type-specific antibodies.

Extracting type 6 group A streptococcai with dilute nitrous acid releases an antigen that exhibits type-specific precipitating properties with anti-M6 serum but fails to neutralize the type-specific bactericidal reaction or to absorb the bactericidal antibody from anti-M6 serum. These studies suggest that the precipitating and antiphagocytic properties of the M protein are attributable to different antigenic determinants. The antigenic determinant responsible for bactericidal antibody is more sensitive to the deleterious effect of nitrous acid than is the moiety responsible for the precipitin reaction. Use of the indirect fluorescent technique with anti-M sera absorbed with lyophilized nitrous acid extracts permits the possible differentiation of the two M-protein determinants in situ on the surface of streptococcal cells.