Repeated Seminal Fluid Exposure Expands Regulatory T Cell Populations in Mice.

Abstract

Regulatory T cells (Treg cells) are required to achieve successful allogeneic pregnancy through their actions in mediating maternal immune tolerance towards conceptus antigens at the time of embryo implantation. In mice, we have shown that seminal fluid exposure is a key factor in maximising the Treg cell pool available systemically and present in the implantation site. Both the seminal plasma and sperm components of seminal fluid contribute to Treg cell activation and proliferation through provision of alloantigens and the immune deviating cytokine transforming growth factor-beta (TGFB), as well as potentially other signalling agents. Additionally, seminal fluid induces uterine expression of chemokines such as CCL19 that facilitate Treg cell recruitment into the uterine endometrium in the peri-implantation period. In women, clinical studies have shown that regular coitus in the absence of barrier methods of contraception over at least a three month period can diminish the incidence of preeclampsia and improve reproductive outcomes. We thus hypothesised that in mice, repeated mating events expand the Treg cell pool beyond that present after a single mating event. To examine the effect of repeated seminal fluid exposure on the maternal Treg cell population, C57BL/6 (B6) female mice were mated once or four times (over a 4-6 week period) to vasectomised (VAS) BALB/c males, then killed on day 3.5 post coitum (pc). Treg cells were quantified by flow cytometry as CD3+CD4+CD25+FoxP3+ cells in the uterus-draining para-aortic lymph nodes, peripheral lymph nodes, spleen and blood. Four matings resulted in an approximately 2-fold increase in the size of the Treg cell population in para-aortic lymph nodes compared with no mating or one mating event. Increases were also seen in the cervical lymph nodes but not the spleen or blood. Surgical removal of the seminal vesicle gland to generate SVX Balb/c males abolished their capacity to elicit expansion of the Treg cell pool. Repeated syngeneic matings of B6 females with VAS B6 males also failed to elicit any further expansion compared with one mating. In conclusion, this study demonstrates that repeated exposure to seminal fluid can expand the Treg cell pool, and that seminal plasma and male alloantigens are involved in eliciting this response. Our findings begin to provide a mechanistic explanation for observations in humans that pregnancy complications are more prevalent after a short duration of sexual relationship or use of barrier methods of contraception. This research was supported by NHMRC Program ID453556 and Fellowship ID627017 awarded to SAR. (platform)