Blocking of antibody complement-dependent effector functions by streptococcal IgG Fc-receptor and staphylococcal protein A.
Using haemolysis in gel, two bacterial IgG-binding substances, an Fc-receptor isolated from group A streptococci type M15, and protein A from Staphylococcus aureus, were shown to inhibit complement-mediated lysis of sheep erythrocytes sensitized with rabbit IgG. When the crude alkaline extracts of ten types of group A streptococci were tested to see whether streptococcal components other than Fc-binding material might affect lysis, the degree of inhibition was found to be correlated with Fc-binding activity. In no case was the lysis of IgM-coated cells inhibited. Opsonophagocytosis experiments showed that both purified streptococcal Fc-receptor and protein A impaired antibody complement-dependent killing by human polymorphonuclear leukocytes of each of two strains of group B streptococci (lacking IgG Fc-receptors). Furthermore, the impairment was ascribable to interference with the fixation of complement to the antibodies, as demonstrated in pre-opsonization experiments with one of the strains. Our results suggest that blocking of the binding of complement to IgG is an important virulence mechanism in Fc-receptor-bearing streptococci and staphylococci.
D000818:Animals; D003165:Complement System Proteins / Q000276:immunology; D004912:Erythrocytes / Q000276:immunology; D006462:Hemolytic Plaque Technique; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology* / Q000378:metabolism; D007075:Immunoglobulin M / Q000276:immunology; D009504:Neutrophils / Q000276:immunology; D009895:Opsonin Proteins / Q000502:physiology; D010587:Phagocytosis; D011817:Rabbits; D011961:Receptors, Fc / Q000276:immunology*; D012756:Sheep; D013205:Staphylococcal Protein A / Q000276:immunology*; D013292:Streptococcus agalactiae / Q000276:immunology; D013297:Streptococcus pyogenes / Q000276:immunology*
D007074:Immunoglobulin G; D007075:Immunoglobulin M; D009895:Opsonin Proteins; D011961:Receptors, Fc; D013205:Staphylococcal Protein A; D003165:Complement System Proteins