Maternal immune tolerance of the semi-allogeneic fetus requires CD4+FOXP3+ T regulatory (Treg) cells to suppress inflammation and anti-fetal immunity. Generation of a robust Treg cell response depends on key cytokines including interleukin 10 (IL10). Mice with a genetic deficiency in IL10 (Il10-/- mice) are susceptible to inflammation-induced fetal loss, but whether Treg cells are involved is not defined.
Female Il10-/- or C57Bl/6 (WT) mice were mated with WT males and killed at different time points during pregnancy. The numbers and phenotypes of Treg cells in the para-aortic lymph nodes (PALN) were examined by flow cytometry. The suppressive function of CD4+CD25+ Treg cells was evaluated in mixed lymphocyte reactions. Treg cell gene expression profiles in Il10-/- and WT controls were determined by Affymetrix microarray and qPCR.
Levels of Treg cells peaked at day 9.5 post coitum with 10-fold higher numbers in KO than WT controls. In vitro, the suppressive competence of CD4+CD25+ Treg cells was unchanged in KO mice, but CD4+ T cells from Il10-/- mice showed greater loss of FOXP3 expression and increased IL17 after stimulation in vitro. Microarray and PCR results demonstrated that several genes associated with inflammation and T cell functions were upregulated in the purified PALN Treg cells of Il10-/- mice recovered in mid-gestation. In particular, the Th1 and Th17 genes Il17a, Il1r1, Il12rb and Ifng were all upregulated 2-5 fold, and Ctse encoding the cytokine-activating enzyme cathepsin E was upregulated >20-fold.
Collectively, these data indicates the pivotal role that IL10 plays in the regulation of Treg cell expansion and stability during pregnancy. We conclude that IL10 is a critical regulator of Treg cell functional competence in pregnancy and that in women, IL10 deficiency may contribute to Treg cell instability, leading to immune-associated pregnancy disorders such as preeclampsia.