Interaction of Haemophilus Influenzae with Complement

Abstract

H. influenzae, whether capsulated or not, is able to activate both the classical and alternative pathways (Anderson et al, 1972; Quinn et al, 1977) resulting in the potential to generate bactericidal and opsonising activities. Most studies have investigated these activities in relationship to type b strains because of the importance of this serotype as a cause of life-threatening invasive infections in childhood. Anderson et al (1972) showed that either purified type b capsular polysaccharide (PRP) or non-capsulated H. influenzae organisms could absorb factors from human serum which were necessary for complement dependent bactericidal activity. Subsequent studies by Steele et al used affinity purified IgG antibodies and agammaglobulinaemic human serum from which factor D and properdin had been selectively inactivated to demonstrate that H. influenzae type b could be killed through classical pathway activities mediated by antibodies to PRP. Similarly, bactericidal activity could also be demonstrated using an IgG fraction from human sera that had been pre-adsorbed with PRP to remove anticapsular antibodies. Taken together, these studies suggested that antibodies to either the PRP capsule or to cell envelope constituents are able to activate the classical pathway and generate bactericidal activity.