title: Inhibition of alternative complement pathway opsonization by group A streptococcal M protein.
abstract: Group A streptococcal M protein is known to be antiphagocytic; however, the exact basis for this property has not been established. In this study the hypothesis was tested that cell wall--associated M protein inhibits phagocytosis by interfering with bacterial opsonization. Two strains of group A Streptococcus pyogenes, CS44 (M+) and CS64 (an M- variant of CS44), were radiolabeled, and after incubation in serum these organisms were exposed to human polymorphonuclear leukocytes. Phagocytosis was quantitated by measurement of leukocyte-associated radioactivity. The contributions of complement and of immunoglobulin to streptococcal opsonization were evaluated by use of serum from a variety of sources. The results revealed that the M- strain was efficiently opsonized via the alternative complement pathway in a relative absence of immunoglobulins. In contrast, the M+ strain was poorly opsonized by all sera tested. These findings suggest that streptococcal M protein in some way prevents bacterial opsonization via the alternative complement pathway and that this property of M protein may partly explain its antiphagocytic characteristic.
mesh_terms: D000942:Antigens, Bacterial / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000494:pharmacology*; D001770:Blood Bactericidal Activity; D002352:Carrier Proteins; D003167:Complement Activation; D003170:Complement Pathway, Alternative; D003171:Complement Pathway, Classical; D004306:Dose-Response Relationship, Immunologic; D014644:Genetic Variation; D006801:Humans; D007074:Immunoglobulin G; D007153:Immunologic Deficiency Syndromes / Q000276:immunology; D008163:Luminescent Measurements; D009504:Neutrophils / Q000382:microbiology; D009895:Opsonin Proteins / Q000276:immunology*; D010587:Phagocytosis; D013297:Streptococcus pyogenes / Q000235:genetics
chemical_list: D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D007074:Immunoglobulin G; D009895:Opsonin Proteins; C014689:streptococcal M protein