Involvement of TLR9 in the Regulation of Immune Tolerance in Early Pregnancy in Murine Abortion-Prone Model

It was shown that toll-like receptors (TLR), in particular TLR4, could participate in the recognition of semen-derived factors, leading to the generation of immune tolerance towards fetal alloantigens [1,2]. This study aimed to examine how inhibition of TLR9 signaling during conception influences costimulatory phenotype of B cells that determines interaction with T cells, how it may impact on B regulatory (Breg) and T regulatory (Treg) cells expansion, conception and abortion rate in the murine abortion-prone model of pregnancy (♀CBA/Jx♂DBA/2 J). ♀CBA/J mice were injected intraperitoneally with 50 µg or 100 µg of the TLR9 antagonist ODN2088 or vehicle after mating with ♂DBA/2 J. At 3 and 14 days post coitum (dpc) costimulatory molecules on B cells, their ligands on T cells, and the frequency of Breg and Treg in the spleen and uterus draining lymph nodes (LN) were examined by a flow cytometry. The pregnancy outcome was determined by the observation of live and resorbed embryos at 14dpc. ODN2088 treated females were characterized by a higher number of resorbed embryos compared to vehicle treated mice. The females also demonstrated downregulation of CD80 (3dpc,14dpc,LN) and upregulation of CD86 on B cells (3dpc,LN), lower expression of CD40L (3dpc,spleen,LN) and CD28 (14dpc,spleen) on T cells as well as a lower percentage of Foxp3+CD25+CD3+CD4+ cells (3dpc,spleen; 14dpc,LN) compared to control mice. The inhibition of a TLR9 signal during mating is associated with an increased risk of pregnancy loss. It is accompanied by a reduction in the Treg pool and by possible alteration of B cell-T cell interaction.