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.
Tarr, PI; Hosea, SW; Brown, EJ; Schneerson, R; Sutton, A; Frank, MM
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