Regulatory T (Treg) cell insufficiency in pregnancy is associated with inflammatory disorders including spontaneous preterm birth (PTB). Emerging evidence suggests periconception events are critical in determining the number and function of Treg cells in later gestation. To assess the importance of early gestation Treg cell responses in PTB susceptibility, we developed a model of Treg cell deficiency in periconception using Foxp3DTR mice, which undergo transient depletion of Treg cells when administered diphtheria toxin (DT).
Foxp3DTR females mated to BALB/c males were administered low dose DT (5-25 ng/g, or vehicle) on gestational day (GD)0.5 and 2.5. Treg cell depletion was tracked by flow cytometry on GD3.5, 6.5, 9.5, and 16.5 (n=4-7/group). Effects on fetal and placental weights and pregnancy viability were evaluated on GD17.5 (n=16-20/group). Treg-depleted and control dams were administered 0, 4, or 8 µg of lipopolysaccharide (LPS) on GD16.5 (n=12-19/group) and video-monitored to measure time of birth.
A dose-dependent effect of DT on Treg cell depletion was demonstrated. Dams given 10-25 ng/g DT exhibited extensive (~95%) systemic Treg cell depletion resulting in reduced pregnancy rates (p=0.011), fewer viable fetuses/dam (p=0.036), growth restricted fetuses (p=0.009), and a decreased fetal:placental weight ratio (p=0.021) on GD17.5. Heightened CD25 expression by CD4+Foxp3- T cells and aberrant lymphocyte proliferation were observed throughout gestation. Greater sensitivity to LPS-induced PTB was seen, such that following 4 µg LPS, Treg-depleted dams had a 20% incidence of early (<GD18) PTB, and a 25% reduction in viable pups/dam, while control dams were unaffected (p=0.027). Both groups exhibited PTB and fetal loss following 8 µg LPS, but this was more pronounced in Treg-depleted dams.
We conclude that periconception Treg cell deficiency impairs late gestation outcomes in mice and increases susceptibility to inflammatory challenge resulting in PTB. This model will increase our understanding of the upstream inflammatory processes causing PTB.