Electron microscopic studies on streptococci. I. M antigen.
The presence of M antigens on group A streptococci is associated with hairlike fimbriae that cover the surface of the streptococcal cell wall and are demonstrable by electron microscopy. These fimbriae also may be associated with R antigen. Like M protein, the surface fimbriae are destroyed by trypsin treatment and reappear when "trypsinized" streptococci are reincubated in fresh, trypsin-free broth. Ferritin-conjugated, type-specific antibodies localize on homologous M+ cells in a pattern suggestive of several M antigenic sites along the length of individual surface fimbria. The M-associated fimbriae remain on the residual cell wall after removal of the bulk of group-specific polysaccharide through nitrous acid extraction. This suggests attachment of the fimbriae to the mucopeptide and minor polysaccharide components remaining in the nitrous acid-extracted wall. The pattern of localization of ferritin-conjugated antibodies on homologous streptococci before and after trypsin exposure and upon reincubation of the trypsinized cells in fresh medium suggests the following hypothesis: M antigen is secreted by the cell, is partially excreted through the otherwise intact cell wall, and is bound by the wall so that M protein occupies a peripheral, exposed position on the surfaces of the streptococcal cell wall.
D000941:Antigens / Q000032:analysis*; D001665:Binding Sites; D002473:Cell Wall; D055598:Chemical Phenomena; D002621:Chemistry; D005293:Ferritins; D007106:Immune Sera; D008854:Microscopy, Electron; D013291:Streptococcus / Q000166:cytology / Q000276:immunology*
D000941:Antigens; D007106:Immune Sera; D005293:Ferritins