Role of hormone-controlled T-cell cytokines in the maintenance of pregnancy.

Human CD4 T helper lymphocytes can be subdivided into at least three distinct functional subsets on the basis of their cytokine secretion profiles. One type of CD4+ lymphocyte, T helper 1 (Th1), produces interferon (IFN)-gamma and tumour necrosis factor beta, a second type (Th2) produces interleukin (IL)-4 and IL-5 and a third type (Th0) produces both Th1 and Th2 cytokines. The apparent paradox that embryos are not rejected by the maternal immune system despite the presence of paternal MHC histocompatibility antigens has been explained in mice by a Th2 switch at the level of the materno-fetal interface. We showed that some hormones enhanced during pregnancy can affect the development of Th1 and Th2 responses. Indeed, we found that progesterone promotes the production of IL-4 and IL-5, whereas relaxin promotes the production of IFN-gamma by T-cells. In addition, we showed that leukaemia inhibitory factor (LIF), which is essential for embryo implantation, associates with Th2 cells and is upregulated by IL-4 and progesterone. We also showed that LIF is down-regulated by Th1 inducers [IL-12, IFN-gamma and IFN-alpha]. Furthermore, we found a decreased production of LIF, IL-4 and IL-10 by decidual T-cells in women with unexplained recurrent abortions in comparison with women with normal gestation at the moment of voluntary abortion. The decreased production of LIF, IL-4 and IL-10 was not found in peripheral-blood T-cells. These results suggest that the local production of LIF and/or Th2 cytokines may contribute to the maintenance of pregnancy.