Target antigens for bactericidal and opsonizing antibodies to Haemophilus influenzae

Three components of Haemophilus influenzae (capsular polysaccharide, lipopolysaccharide and proteins of the outer membrane) were studied concerning their possible rôle as target antigens for bactericidal and opsonizing antibodies. In rabbit antisera against capsulated H. influenzae the bactericidal antibodies were mainly directed against the capsular polysaccharide but also, to a smaller extent, against the outer membrane antigens. Using a non-capsulated mutant of H. influenzae type b it was demonstrated that both the lipopolysaccharide and the proteins of the outer membrane are target antigens for bactericidal antibodies. In antisera against whole bacteria antibodies against the lipopolysaccharide and the outer membrane, proteins were in equal concentrations, while in antisera against the outer membrane a greater proportion of the bactericidal antibodies were directed against the lipopolysaccharide. Some of the outer membrane target proteins for bactericidal antibodies were common to various serotypes of H. influenzae. The capsular polysaccharide as well as the lipopolysaccharide and the proteins of the outer membrane constituted target antigens also for opsonizing antibodies to capsulated H. influenzae type b.