Vaccination with the Chlamydia trachomatis Major Outer Membrane Protein Can Elicit an Immune Response as Protective as That Resulting from Inoculation with Live Bacteria

ABSTRACT

BALB/c mice were vaccinated by the intramuscular (i.m.) and subcutaneous (s.c.) routes with a native preparation of the Chlamydia trachomatis mouse pneumonitis (MoPn) major outer membrane protein (MOMP), using Montanide ISA 720 and CpG-1826 as adjuvants. A negative control group was immunized with ovalbumin and the two adjuvants, and a positive control group was immunized intranasally (i.n.) with 10⁴ inclusion-forming units (IFU) of C. trachomatis. Four weeks after the last i.m.-plus-s.c. immunization, mice were challenged in the ovarian bursa with 10⁵ IFU of C. trachomatis MoPn. Six weeks after the genital challenge, animals were mated, and the pregnancies were monitored. After vaccination with MOMP, the mice developed strong Chlamydia-specific humoral and cellular immune responses. Following the genital challenge, of the mice vaccinated with the MOMP, only 15% (3/20) had positive vaginal cultures, while 85% (17/20) of the animals immunized with ovalbumin had positive cultures over the 6 weeks of observation (P < 0.05). Also, only 14% (3/21) of the animals inoculated i.n. with Chlamydia had positive vaginal cultures. After mating, 75% (15/20) of the mice vaccinated with MOMP carried embryos in both uterine horns. Of the animals vaccinated i.n. with the Chlamydia, 81% (17/21) had embryos in both uterine horns (P > 0.05). In contrast, only 10% (2/20) of the mice immunized with ovalbumin had embryos in both uterine horns (P < 0.05). In conclusion, immunization with a purified preparation of the MOMP is as effective as vaccination with viable C. trachomatis in eliciting a protective immune response against a genital challenge in mice.