title: Alternate complement pathway activation by group A streptococci: role of M-protein.
abstract: Avirulent strains of group A streptococci readily activate the complement system in normal human serum via the alternate complement pathway (ACP). Virulent M-positive group A streptococci are much less potent as activators of the ACP. The ability of M-positive streptococci to activate the ACP is enhanced by trypsinization or mild peptic digestion. The latter treatment removes the serologically active and antiphagocytic type-specific moieties of M protein, but retains the surface fuzzy layer. The phagocytosis of avirulent streptococci is markedly enhanced by preopsonization in serum chelated with Mg-ethylene glycol tetraacetic acid (classic complement pathway blocked) but not in serum devoid of heat-labile factors. These studies suggest that the function of M protein as a virulence factor may be mediated, at least in part, by its ability to retard interaction of ACP components with structures present on the streptococcal cell surface.
mesh_terms: D001426:Bacterial Proteins / Q000276:immunology*; D003167:Complement Activation / Q000187:drug effects; D003170:Complement Pathway, Alternative; D006801:Humans; D006821:Hyaluronoglucosaminidase / Q000494:pharmacology; D009895:Opsonin Proteins; D010434:Pepsin A / Q000494:pharmacology; D013297:Streptococcus pyogenes / Q000276:immunology*; D014357:Trypsin / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D009895:Opsonin Proteins; D006821:Hyaluronoglucosaminidase; D014357:Trypsin; D010434:Pepsin A