title: Resistance to phagocytosis by group A streptococci: failure of deposited complement opsonins to interact with cellular receptors.
abstract: The previous finding that phagocytosis-resistant M+ group A streptococci bear quantities of C3 which are sufficient for phagocytosis of their M- derivatives was investigated at two levels. It was first established that the C3 associated with M+ streptococci was not able to promote adherence to cells bearing the complement receptors CR1 and CR3 under conditions in which M- streptococci readily attached. The molecular form of C3 bound to M+ and M- streptococci was then defined by adding 125I-C3 to serum used for opsonization. C3 eluted from the bacteria by chaotropic and hydrolytic agents was analyzed by SDS-PAGE, and revealed that both cell types bound the opsonic forms of C3, C3b, and iC3b. Furthermore, approximately 80% of the C3b and iC3b associated with both cell types was covalently bound to a surface component, although most of the C3 bound to M+ streptococci was detergent-extractable, whereas greater than 50% of that bound to M- streptococci was not. These findings demonstrate that the M+ surface is interfering with the receptor binding of deposited C3b and iC3b, and that this contributes to resistance to phagocytosis by these organisms.
mesh_terms: D003167:Complement Activation; D003176:Complement C3 / Q000276:immunology / Q000302:isolation & purification; D003165:Complement System Proteins / Q000276:immunology*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008970:Molecular Weight; D009504:Neutrophils / Q000276:immunology; D009895:Opsonin Proteins / Q000276:immunology*; D010587:Phagocytosis; D013297:Streptococcus pyogenes / Q000276:immunology*
chemical_list: D003176:Complement C3; D009895:Opsonin Proteins; D003165:Complement System Proteins