Development of serum bactericidal activity following nontypable Haemophilus influenzae acute otitis media

We monitored the development of serum bactericidal antibody in eight children with acute nontypable Haemophilus influenzae otitis media and correlated its development with the appearance of antibody against lipooligosaccharide and surface-exposed outer membrane proteins of the infecting strains. Complement-dependent bactericidal activity was absent in acute sera but increased to titers of 1:4 to 1:32 in sera obtained 4 to 6 weeks later. Absorption of anti-lipooligosaccharide antibodies from convalescent sera had no effect on bactericidal titers of five patients and resulted in small decreases in titer in three patients. Lipooligosaccharide-absorbed samples had persisting bactericidal titers of 1:4 to 1:16. Four of eight acute samples lacked antibodies to surface-exposed outer membrane proteins whereas four had low concentrations of antibody directed against one or more Mr 100,000 to 250,000 outer membrane proteins. Convalescent samples from all eight children showed substantial increases in antibodies directed primarily against Mr 100,000 to 250,000 proteins. Thus, both surface-exposed Mr 100,000 to 250,000 outer membrane proteins and lipooligosaccharide are immunogenic during Haemophilus otitis media and are potential targets of bactericidal antibody.