A RESOLVED PNEUMOCOCCAL INFECTION PROTECTS AGAINST NONTYPABLE HAEMOPHILUS-INFLUENZAE - AN EVALUATION OF DIFFERENT ROUTES OF WHOLE-CELL IMMUNIZATION IN PROTECTION AGAINST EXPERIMENTAL ACUTE OTITIS-MEDIA

A conferred cross-protection between Haemophilus influenzae type b (Hi b) and nontypeable H.influenzae (NTHi) was demonstrated in a previous study of experimental recurrent otitis media. To explore cross-protect ion further, and to compare oral administration of whole cells with tw o more conventional routes for vaccination against acute otitis media (AOM), a total number of 79 rats were immunized perorally, subcutaneou sly and intrabullarly with H. influenzae or pneumococci and thereafter challenged in the middle ear with NTHi or Hib 4 or 9 weeks later. Oto microscopic changes, bacterial cultures, and serum IgG antibody levels were monitored. The study demonstrated that while peroral administrat ion did not elicit any protection, a resolved pneumococcal AOM could r educe the susceptibility to reinfection with NTHi. In the latter case no cross-reacting antibodies were detected, but the protective rate wa s 50% or more, and it was comparable with that found after subcutaneou s or intrabullar immunization with homologous NTHi or Hib strains. The results suggest that the protection of the rat middle ear mucosa may involve unspecific responses. (C) 1997 Elsevier Science Ireland Ltd.