EVALUATION OF MIXTURES OF PURIFIED HAEMOPHILUS-INFLUENZAE OUTER-MEMBRANE PROTEINS IN PROTECTION AGAINST CHALLENGE WITH NONTYPABLE HAEMOPHILUS-INFLUENZAE IN THE CHINCHILLA OTITIS-MEDIA MODEL

Nontypeable Haemophilus influenzae (NTHi) is one of the leading causat ive agents of bacterial otitis media, and no vaccine has been shown to be effective against it. Three outer membrane lipoproteins of NTHi ha ve been investigated extensively and are leading candidates for inclus ion in a vaccine against this organism. Hi-PAL (P6), recombinant PCP ( rPCP), and e (P4) proteins are antigenically conserved among NTHi stra ins and elicit bactericidal and protective antibodies. A genetic fusio n of the rPCP and Hi-PAL proteins has also been reported. Mixtures of these proteins were used for active immunization experiments in the ch inchilla model of otitis media. Chinchillas were immunized either with a mixture of all three lipoproteins or with the mixture of rPCP-PAL h ybrid plus e protein. When these animals were challenged with a NTHi s train injected directly into the middle ears, no protection from infec tion or disease, as measured by otoscopy, was observed in either group . However, effusion and inflammation measured by tympanometry were sig nificantly reduced in animals immunized with the three lipoproteins. A nimals that had been immunized with either whole NTHi cells or total o uter membranes and then challenged with the homologous strain were sig nificantly protected from both infection and disease, as determined by tympanometry and otoscopy. Unlike other animal antisera, chinchilla a ntisera against the purified proteins had no bactericidal activity aga inst NTHi but did fix complement on the cell surface. Thus, the chinch illa immune responses to mixtures of these lipoproteins differ from th e immune responses observed in other animal species. Further evaluatio n of these proteins for their vaccine potential remains to be done.