The importance of being a regulatory T cell in pregnancy

Natural Foxp3+ regulatory T cells (nTregs) defined by expression of the Foxp3 marker generated in the thymus against self autoantigens prevent systemic autoimmune and inflammatory disease. A second population of Tregs induced by exogenous antigens in the periphery (iTregs) are currently thought to play a key role in preventing infertility, recurrent pregnancy loss (occult and clinically-evident), pre-eclampsia, fetal growth restriction, and premature birth in outbred matings where the father is histoincompatible with the mother. Curiously, when iTregs are ablated in mice, fertility is usually not impaired and resorption rates in matings with allogeneic males can range from 0% to 100% in individual females. Analysis of possible explanations suggest iTregs prevent abortions by countering effects of environmental stressors. Depletion of iTregs at mid-pregnancy in mice only causes abortions in an artificial transgenic model. Effects of iTreg depletion on pre-eclampsia, fetal growth restriction, and premature birth remain to be tested. Tregs induced during pregnancy may also affect the health of offspring in post natal life as well as the health of the mother.