Immunization with the Chlamydia trachomatis mouse pneumonitis major outer membrane protein can elicit a protective immune response against a genital challenge

Infertility, ectopic pregnancy, and chronic abdominal pain are frequent com plications of genital infections with Chlamydia trachomatis. In an attempt to produce a vaccine to protect against this pathogen we purified and refol ded the C. trachomatis mouse pneumonitis (MoPn) major outer membrane protei n (MOMP). This preparation, mixed with Freund's adjuvant using vortexing or sonication, was used to immunize BALB/c mice that were subsequently challe nged in the upper genital tract. Vaginal cultures were taken on a weekly ba sis, and mice were mated 6 weeks after the challenge. Gels of the vortexed MOMP showed a predominant band with a molecular size of 62 kDa and weaker b ands at 42 and 132 kDa, while the sonicated MOMP had a single band with a m olecular size of 42 kDa. Following immunization with these two preparations , strong Immoral and cell-mediated immune responses were detected in the mi ce inoculated with the vortexed MOMP. On the other hand, mice immunized wit h the sonicated MOMP had a strong Immoral immune response but a relatively weak cell-mediated immune response, as determined by a T-cell lymphoprolife rative assay and level of cytokine production by splenocytes. Vaginal cultu res showed that the mice immunized with the vortexed MOMP were significantl y protected, as determined by a decrease in the number of animals with posi tive cultures, the length of time the mice shed viable organisms, and the n umber of inclusion-forming units recovered per mouse. Animals immunized wit h the sonicated MOMP, on the other hand, showed a weaker level of protectio n based on the same three parameters. After mating, the number of fertile a nimals and number of embryos per mouse were significantly higher for the mi ce immunized with vortexed MOMP, but not for the mice immunized with sonica ted MOMP, compared to those of the control groups. In conclusion, immunizat ion with a purified and refolded preparation of the C. trachomatis MoPn MOM P confers a significant level of protection in mice against a genital chall enge.