Chlamydia trachomatis infection in the female reproductive tract of the rat: influence of progesterone on infectivity and immune response

Abstract

As the most common cause of sexually transmitted disease in women, chlamydial infections can lead to pelvic inflammatory disease, infertility, and ectopic pregnancy. To better understand the role played by sex hormones in modulating the immune response of the genital tract to microbial infections, we have developed a rat model to study Chlamydia trachomatis infection. Inbred female Lewis rats were primed with progesterone and inoculated by intrauterine instillation of C. trachomatis (mouse pneumonitis strain MoPn) into each uterine horn. When infected animals were examined for the presence of chlamydial antigens 14 days postinfection, both the uterus and vagina were found to be positive compared to those of saline-treated animals, which did not show specific staining. The involvement of local and systemic immune systems following chlamydial infection was determined by analyzing major histocompatibility complex (MHC) class II expression in the reproductive tract and lymphocyte proliferation in response to mitogenic and chlamydia-specific stimulation of cells from the spleen and lymph nodes (LN) draining the reproductive tract. Enhanced proliferation was observed in LN following mitogenic but not antigenic (MOMP [major outer membrane protein]) stimulation. In contrast, spleen cell proliferation was lower in chlamydia-infected rats than in saline-treated controls. MHC class II expression, an indicator of inflammatory responses, was upregulated in the uterus, on glandular epithelial cells, and adjacent to glands in response to chlamydial infection. In other experiments, when rats were infected at estrus and diestrus without prior progesterone priming, chlamydial inclusions were not detected in either the uterus or vagina. However, enhanced lymphocyte proliferation was observed in response to mitogenic and MOMP stimulation in the reproductive tract-draining LN from estrous and diestrous animals. These findings indicate that under appropriate endocrine conditions, the rat uterus is susceptible to C. trachomatis infection and that immune responses to this pathogen can be detected locally and systemically. Further, they suggest that clearance of the infection from the reproductive tract involves immune cells from the LN draining the reproductive tract.

FIG. 1

Localization of chlamydial antigen by immunochemistry in uteri and vaginas of progesterone-treated rats inoculated with chlamydiae. Polyclonal antichlamydia antibody (1:200) was used to detect chlamydia-specific staining. Positive staining is seen in the epithelium of both uterus (A) and vagina (C). Controls shown are uterus (B) and vagina (D) from saline-treated animals stained with the same antibody. s, stroma; g, gland; lu, lumen; e, epithelium. Bars, 80 μm.

FIG. 2

MHC class II-positive cells in uteri of progesterone-treated rats inoculated with chlamydiae (A) and saline (B). Class II expression is upregulated in the uteri of chlamydia-treated animals compared to saline-treated rats. lu, lumen. Bars, 80 μm.

FIG. 3

LN (A) and spleen (B) cell proliferation on day 14 in response to mitogens and MOMP in progesterone-treated, control (saline-inoculated), and chlamydia-infected animals. Three to five animals were used for each treatment group. Results shown are representative of four separate experiments. Experimental groups consist of LN or spleen cells incubated in the presence of control (medium alone) (bar 1), ConA (bar 2), PHA (bar 3), LPS (bar 4), and MOMP at 1 (bar 5), 5 (bar 6), and 10 (bar 7) μg/ml. ∗, P < 0.05.

FIG. 4

Localization of chlamydial antigen by immunochemistry in uteri of rats inoculated with chlamydiae at estrus (A) or diestrus (B). No positive staining could be detected in the uterus at either stage with a chlamydia-specific polyclonal antibody. Bars, 80 μm.

FIG. 5

(A and B) LN proliferation on day 14 in response to mitogens in animals treated with chlamydiae at estrus (A) and diestrus (B). (C) MOMP-specific proliferation in rats exposed to saline or chlamydiae at estrus or diestrus. Three to five animals were used for each treatment group. Results shown are representative of two separate experiments. ∗, P < 0.05.

FIG. 6

LN proliferation on day 3 in response to mitogens and MOMP in animals infected with chlamydiae following progesterone pretreatment (A), at estrus (B), and at diestrus (C). Three to five animals were used for each treatment group. Results shown are representative of two separate experiments. Experimental groups consist of LN cells incubated in the presence of control (medium alone) (bar 1), ConA (bar 2), PHA (bar 3), LPS (bar 4), and MOMP at 1 (bar 5) and 5 (bar 6) μg/ml. ∗, P < 0.05.