Streptococcal M Protein Extracted by Nonionic Detergent

Streptococcal M proteins are antiphagocytic molecules varying immunologically from type to type while maintaining an identical biological effect. The virulence of the group A streptococcus is directly related to the presence of the M antigens on the cell surface and resistance to infection by these organisms is dependent on the presence of opsonic antibodies directed towards the M molecules. Various methods such as latex agglutination (1), hemagglutination (2, 3), complement fixation (4), mouse protection (5), capillary precipitation (6), longchaining tests (7), and radioimmunoassays (8, 9), have been used to determine the immune response to the M antigens. Despite this variety of alternative methods, the only generally acceptable and reliable measurement of typespecific opsonic antibodies in the serum is the standard bactericidal test (5). The occurrence of cross-reactions has precluded the replacement of the cumbersome bactericidal assay for the measurement of type-specific immunity to streptococcal infection with one of the other in vitro techniques. The reason for these difficulties may be twofold: (a) the state of the M antigen used in the assay, and (b) the inherent nature of the protein antigen itself. The occurrence of cross-reactions has usually been attributed to unrelated antigens physically or chemically associated with the M protein (10-12). Although the M preparations used in many of these studies may well have contained other cellular antigens, an alternate explanation for these cross-reactions may be based on the presence of common regions in the polypeptide chain of certain M types (13-16). In the present communication, a radioimmunoassay and solid-phase radiocompetitive inhibition experiments are used to examine the antibodies developed against M6 protein in both human beings and hyperimmunized rabbits. By these techniques, the nature of a type-specific opsonic response and its relation to cross-reactions were examined on a molecular level.