1062 PROTECTION BY SERUM ANTIBODIES IN EXPERIMENTAL NONTYPABLE HAEMOPHILUS INFLUENZAE (NTHI) OTITIS MEDIA (OM)

Abstract

Host immune defenses appear to be important in the prevention of NTHI OM. I investigated the importance of serum antibodies in prevention of experimental OM in chinchillas. Animals infected by unilateral intrabullar inoculation with 103 cfu of NTHI strain 3245 uniformly developed acute OM. Following recovery, animals were protected against rechallenge with the homologous organism. Immunity was associated with the appearance of serum antibodies directed primarily against a 39Kd surface-exposed major outer membrane protein (OMP) as determined in a whole-cell radioimmunoprecipitation (WC-RIP) assay. Antibodies to LPS were undetectable in convalescent sera by ELISA. In a second experiment, chinchillas were immunized with killed bacteria. Pooled preimmune or immune serum from these animals was administered to a second group of animals one day prior to intrabullar bacterial challenge. 5 of 5 animals receiving preimmune serum developed OM compared to 0 of 10 animals receiving immune serum (P<.001). The immune serum pool and sera from passively immunized animals contained antibodies directed primarily against the 39Kd OMP by WC-RIP. AntiLPS antibody was detectable in the immune serum pool and in sera from passively protected animals. However, the antiLPS ELISA titer was more than 10-fold lower than the titer to the 39Kd OMP. Neither convalescent sera from infected animals nor sera from immunized animals was bactericidal. My results indicate that serum antibody is protective in experimental NTHI otitis, possibly by means of opsonic activity, and that major OMPs or LPS may be important immune targets.