Maternal immune tolerance of the semi-allogeneic fetus requires CD4+FOXP3+ T-regulatory (Treg) cells, which suppress inflammation and anti-fetal immunity. Expansion of the Treg cell pool in preparation for conception is mediated by seminal fluid. Recent studies have demonstrated that microRNAs contribute to Treg cell function with miR155 established as a key Treg cell miRNA. However, the physiological importance of miR155 in early pregnancy and Treg expansion, and whether miR155 contributes to pregnancy success is unknown.
CBA x C57Bl/6 F1 female mice (n=8-10) were mated with Balb/c males and sacrificed at 8, 16, 36, 60 and 84h post-coitus (pc). Uterine-draining lymph nodes (PALN) were collected and miRNA expression levels were determined using qPCR. miR155-/-or wildtype (WT) females (n=11-13) were mated with Balb/c males and sacrificed on day 3.5 pc. The percentage of Treg cells in the mesenteric lymph nodes(mLN), spleen, blood and PALN was examined by flow cytometry. Pregnant miR155-/-or WT (n=20-23) females were sacrificed on day 17.5pc, fetal and placental weights were determined to assess pregnancy outcome.
Exposure to seminal fluid suppressed miR155 expression in PALN throughout the peri-conception period with the most significant reduction (2.5-fold) observed 8h pc. miR155 deficiency resulted in a systemic reduction in the percentage of Treg cells compared to the WT control with the most significant reduction being observed in the PALN (2.6-fold). Maternal miR155 deficiency altered the outcomes of pregnancy with a 6.0% increase in fetal weight and 7.9% increase in the fetal:placental ratio in late gestation.
In conclusion, seminal fluid suppresses miR155 during early pregnancy and the absence of miR155 is associated with reduced Treg cell proportions, and may lead to altered fetaland placental development. These data indicate a potentially important role for miR155 in the expansion of Treg cellsduring early pregnancy, and may provide novel diagnostic therapies for Treg-associated pregnancy pathologies.