STREPTOCOCCAL M ANTIGEN LOCATION AND SYNTHESIS, STUDIED BY IMMUNOFLUORESCENCE

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Abstract
Trypsinization of live Group A streptococci resulted in loss of M, verified by non-staining with homologous type-specific (anti-M) fluorescent antibody. After reincubation M reappeared only at sites of new cell wall formation and not in or on old wall. In deficient medium, limited new wall formation and associated M synthesis varied with the strain, although it was sometimes enough to allow detection of M by serologic methods concomitant increases in optical density were not detected. Encapsulated strains incubated in group- or type-specific fluorescent antibodies failed to show capsular fluorescence, although antibody penetration of capsules revealed fluorescence of wall antigens. Prior adsorption by streptococci of unlabeled homologous type-specific antibody blocked later staining by both group and homologous type fluorescent antibodies: unlabeled group antibody, however, blocked only group and not type-specific immunofluorescence. These results confirm the surface location of M antigen. Its antigenic determinants appear to be superficial to the group substance, and neither was shown in capsules. M synthesis after trypsinization occurs only where new wall is forming and is not, therefore, "resynthesis", as previously believed.