Bactericidal antibodies against noncapsular components of Haemophilus influenzae

Bactericidal antibodies against components of Haemophilus influenzae other than the capsular polysaccharide were analyzed in sera from patients infected with this organism and compared with the antibody levels in sera from a normal population. Such antibodies could be demonstrated in sera from about one-third of patients infected with H. influenzae type b, including children less than 1 year old. It is possible that these antibodies were directed against outer membrane proteins, since they persisted after absorption with capsular polysaccharide type b and lipopolysaccharide. These findings suggest a protective role for antibodies directed against outer membrane components, possibly proteins, in infections caused by capsulated strains of H. influenzae.