Antibodies to Haemophilus influenzae and their bactericidal activity / Teresa Dahlberg-Lagergård.

Tese (doutor) - University of Göteborg, 1982

A bactericidal (BC) assay and an enzyme-linked immunosorbent assay (ELISA) were developed and employed together with other serological methods (opsonizing assay, indirect hemagglutination assay and complement fixation assay) to study antibodies to Haemophilus influenzae in immunized rabbits and infected humans. Rabbits immunized with capsulated and noncapsulated bacteria responded with BC antibodies within a week after the primary dose. Repeated immunizations raised the BC titres of antisera against capsulated bacteria to very high levels; BC titres against noncapsulated bacteria also increased but to a lower level. Antibodies to capsulated polysaccharide (CPS) and to lipopolysaccharide (LPS) in primary response antisera (rabbits immunized with capsulated or noncapsulated bacteria) were mainly of IgM class as tested by ELISA. After repeated immunizations both IgM and IgG class antitodies were present in all sera. Different cell surface components of H. influenzae were studied concerning their possible role as target antigens for BC and opsonizing antibodies. In rabbit antisera against capsulated bacteria the BC antibodies were mainly directed against CPS but also to a smaller extent against outer membrane antigens. Using a noncapsulated mutant of H. influenzae type b, it was demonstrated that both LPS and outer membrane proteins probably are target antigens for BC antibodies. CPS, LPS and outer membrane proteins were target antigens also for opsonizing antibodies to capsulated H. influenzae type b. In humans, antibodies to CPS of H. influenzae type b were lowest in serum samples from healthy children of 1-11 months of age; thereafter the mean titre increased with age and reached adult levels in children more than 6 years old. A BC antibody response associated with a significant response ,to CPS type b was observed in the majority of patients with H. influenzae type b infections. BC antibodies against other components than CPS were demonstrated in sera from about one third of the infected patients: these antibodies persisted after absorption with CPS and LPS suggesting that they were directed against outer membrane proteins. Secretory component--containing antibodies to CPS were detected in one half of nasopharynx secretions and in the majority of milk samples analysed.