UC Irvine

Chlamydia trachomatis is the leading cause of infection-induced infertility in women. Attempts to control this epidemic with screening programs and antibiotic therapy have failed. Currently, a vaccine to prevent C. trachomatis infections is not available. In order to develop an animal model for evaluating vaccine antigens that can be applied to humans, we used C. trachomatis serovar D (strain UW-3/Cx) to induce infertility in mice whose major histocompatibility complex class II antigen was replaced with the human leukocyte antigen DR4 (HLA-DR4). Transcervical inoculation of medroxyprogesterone-treated HLA-DR4 transgenic mice with 5 × 10⁵C. trachomatis D inclusion forming units (IFU) induced a significant reduction in fertility, with a mean number of embryos/mouse of 4.4 ± 1.3 compared to 7.8 ± 0.5 for the uninfected control mice (P < 0.05). A similar fertility reduction was elicited in the wild-type (WT) C57BL/6 mice (4.3 ± 1.4 embryos/mouse) compared to the levels of the WT controls (9.1 ± 0.4 embryos/mouse) (P < 0.05). Following infection, WT mice mounted more robust humoral and cellular immune responses than HLA-DR4 mice. As determined by vaginal shedding, HLA-DR4 mice were more susceptible to a transcervical C. trachomatis D infection than WT mice. To assess if HLA-DR4 transgenic and WT mice could be protected by vaccination, 10⁴ IFU of C. trachomatis D was delivered intranasally, and mice were challenged transcervically 6 weeks later with 5 × 10⁵ IFU of C. trachomatis D. As determined by severity and length of vaginal shedding, WT C57BL/6 and HLA-DR4 mice were significantly protected by vaccination. The advantages and limitations of the HLA-DR4 transgenic mouse model for evaluating human C. trachomatis vaccine antigens are discussed.