The regulatory role of thymic stromal lymphopoietin (TSLP) in maternal–fetal immune tolerance during early human pregnancy

Thymic stromal lymphopoietin (TSLP) is an IL-7-like cytokine, and the functional TSLP receptor (TSLPR) consists of a common IL-7 receptor alpha chain (IL-7Rα) and TSLP-specific gamma receptor chain (TSLPR-γ). It has been demonstrated that TSLP plays an important role in the Th2 bias and regulatory T cell expansion of immune respose and tolerance. A successful pregnancy, especially in the early phase, demonstrates features of a Th2 immune response and requires CD4+Foxp3+ regulatory T cell expansion. We have found recently that TSLP-instructed decidual dendritic cells (dDCs) promote decidual CD4+ T cells to produce Th2-type cytokines including IL-10, which is believed to be a key player in maternal–fetal tolerance. Phenotypic analyses have shown that the expanded cells are mainly CD4+ Th2 cells and Foxp3+ regulatory T cells. Our findings show that trophoblasts secrete TSLP that is able to instruct the dDCs to induce CD4+ Th2 cell and Foxp3+ regulatory T cell differentiation in decidual CD4+ T cells.