The requirement of specific anticapsular IgG for killing of Haemophilus influenzae by the alternative pathway of complement activation.
Employing an in vitro bactericidal assay using C4-deficient guinea pig serum (C4D-GPS), we evaluated the ability of the alternative pathway to kill a number of strains of encapsulated and unencapsulated Haemophilus influenzae (HI). Complement activation occurred, but no bactericidal activity was observed against any of the tested HI in nonimmune C4D-GPS without detectable antibody to HI-type b (HIb) capsular polysaccharide (HIb-ps). In the presence of high-titered human anti- (type b) IgG, C4D-GPS killed the encapsulated strains. Restoration of classical pathway activity by the addition of purified C4 to C4D-GPS, which contained antibody to somatic antigens, resulted in killing of some strains of both encapsulated and unencapsulated HI. In nonimmune C4D-GPS the alternative pathway is activated but does not mediate bactericidal activity. The addition of specific high-titered anticapsular IgG results in killing of encapsulated HI by the alternative pathway in guinea pig serum.
D000818:Animals; D000907:Antibodies, Bacterial / Q000096:biosynthesis; D001770:Blood Bactericidal Activity; D003167:Complement Activation; D003176:Complement C3 / Q000378:metabolism; D003181:Complement C4 / Q000172:deficiency; D003170:Complement Pathway, Alternative; D003171:Complement Pathway, Classical; D006168:Guinea Pigs; D006192:Haemophilus Infections / Q000276:immunology*; D006193:Haemophilus influenzae / Q000276:immunology; D006801:Humans; D007106:Immune Sera / Q000276:immunology; D007074:Immunoglobulin G / Q000096:biosynthesis*; D011135:Polysaccharides, Bacterial / Q000276:immunology
D000907:Antibodies, Bacterial; D003176:Complement C3; D003181:Complement C4; D007106:Immune Sera; D007074:Immunoglobulin G; D011135:Polysaccharides, Bacterial