PARTIAL PROTECTION AGAINST GENITAL REINFECTION BY IMMUNIZATION OF GUINEA-PIGS WITH ISOLATED OUTER-MEMBRANE PROTEINS OF THE CHLAMYDIAL AGENTOF GUINEA-PIG INCLUSION CONJUNCTIVITIS

Because partial protection against reinfection is induced by experimen tal infection in the guinea-pig model of genital chlamydial infection, we sought to induce immunity by immunization. Female guinea-pigs were immunized subcutaneously with the major outer-membrane protein (MOMP) and the 61 kDa cysteine-rich outer-membrane protein (61 kDa) of the a gent of guinea-pig inclusion conjunctivitis (GPIC) eluted from SDS-pol yacrylamide gels (SDS-MOMP, SDS-61 kDa). Post-immunization sera and se cretions contained antibodies to the SDS-purified proteins at high tit re as measured by immunoblotting, whereas enzyme inmunoassays (EIA) us ing whole elementary bodies as antigen showed significantly lower titr es (P < 0.001). Likewise, blastogenic responses of peripheral mononucl ear cells to GPIC elementary bodies were weak. Animals immunized with SDS-MOMP and SDS-61 kDa were fully susceptible to intravaginal challen ge, as were control animals immunized with buffer without protein. Ano ther group of animals were immunized with material prepared by extract ion of chlamydial outer-membrane complexes with octyl P-D-glucopyranos ide (OGP) and dithiothreitol, which consisted largely of MOMP (OGP-MOM P). In contrast to the SDS-MOMP group, sera and secretions in the OGP- MOMP group showed high titres in EIA, and high titre antibodies to MOM P by immunoblot; however, most animals also had antibodies to 61 kDa, 72 kDa and ca. 84 kDa outer-membrane proteins. OGP-MOMP animals were p artially protected against genital challenge as evidenced by low inclu sion scores compared to control animals, although duration of infectio n measured by culture isolation was similar to controls. Immunoblot an alysis of sera from immunized animals and from a group of immune anima ls post-infection was performed using recombinant fusion peptides cont aining the four variable domains of MOMP. No consistent differences in reaction patterns were observed when sera from protected and non-prot ected animals were compared. Thus, a highly refined outer-membrane pre paration is capable of producing partial immunity to genital infection . Further study is required to determine whether the protection is due to MOMP itself or to other outer-membrane proteins found in small amo unts in the OGP-MOMP immunogen. The results suggest the possibility th at discontinuous MOMP epitopes could play a role in inducing a protect ive immune response in the guinea-pig model, a concept that requires f urther evaluation.