Maternal immune tolerance of the semi-allogeneic fetus requires CD4+Foxp3+ T-regulatory (Treg) cells, which suppress inflammation and anti-fetal immunity. In mice, expansion of the Treg cell pool is initiated by seminal fluid contact at coitus. Recent studies have demonstrated that microRNAs (miRNA) including miR-223 play a role in the regulation of immune responses. This study aimed to investigate the contribution of miR-223 to maternal immune environment, by evaluating Treg cell and antigen presenting cell activation and proliferation using flow cytometry in miR-223-/- or miR-223+/+ C57Bl/6 females at estrus or d3.5pc mated to Balb/c males (n=10-15/group). miR-223 deficiency resulted in a significant alteration in the Treg cell profile in early pregnancy in the PALN following mating where reductions were observed in the proportion of Treg cells amongst the CD4+ T cell pool (22%, p<0.05) and Treg number (28%, p< 0.05) compared to mated miR-223+/+ females. In the absence of miR-223, a reduction in macrophages as a proportion of total cells (58%, p<0.05) and in the number of activated macrophages (15%, p<0.05) was observed in the PALN on d3.5pc compared to mated miR-223+/+ mice. Additional miR-223-/- and miR-223+/+ mice (n=20=21/group) were administered low dose LPS on d9.5pc, to evaluate pregnancy outcomes. The absence of miR-223 led to altered outcomes in pregnancy following LPS inflammatory challenge, with an 10% reduction in fetal weight and a 19% reduction in the fetal:placental weight ratio in late gestation. LPS administration also significantly increased the resorption rate (8.78-fold, p<0.05) in miR-223-/- females compared to miR-223+/+ females.
Collectively, these data show that the absence of miR-223 alters the maternal immune profile in early pregnancy and this may increase susceptibility to inflammation-induced fetal loss later in gestation. These findings may be relevant to understanding how Treg-associated pregnancy pathologies such as preeclampsia arise in women where reduced miR-223 has been noted.