M proteins of group G streptococci: mechanisms of resistance to phagocytosis.
Group G streptococci that express M protein and resist phagocytosis in human blood (virulent strains) were compared with strains of groups G and A that are readily phagocytosed (avirulent). Virulent group G streptococci were less effective (P < .05) as activators of the alternative complement pathway (ACP) than were avirulent streptococci. In immunofluorescence studies, C3 bound more avidly to avirulent than to virulent group G streptococci. Resistance of virulent group G strains to ACP opsonization and to phagocytosis was markedly diminished by removal with pepsin of the type-specific portion of the M molecule. Preincubation with fibrinogen did not diminish ACP activation or C3 binding by virulent group G and A streptococci but did exert an antiphagocytic effect. Given the similarity of M proteins of groups G and A in structure and function, other microbial constituents are likely responsible for differences in the spectra of illnesses attributable to the two serogroups.
Campo
R E
RE
Department of Medicine, University of Miami School of Medicine, Florida.
Schultz
D R
DR
Bisno
A L
AL
D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000276:immunology*; D002352:Carrier Proteins; D003176:Complement C3 / Q000276:immunology; D003170:Complement Pathway, Alternative; D005340:Fibrinogen / Q000502:physiology; D006801:Humans; D010587:Phagocytosis; D013291:Streptococcus / Q000276:immunology*
D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D003176:Complement C3; C014689:streptococcal M protein; D005340:Fibrinogen