Angiogenic and immune tolerance function of hCG. hCG has many angiogenic functions such as stimulation of VEGF production, trophoblast invasion and proliferation of endothelial cells. By stimulating IL-10 and IDO expression, promoting uNK cell proliferation and Treg cell migration, hCG may play a role in immune tolerance at the maternal fetal interface. VEGF: vascular endothelial growth factor, hCG: human chorionic gonadotropin, IL-10: interleukin-10, IDO: indoleamine 2,3-dioxygenase, uNK: uterine natural killer cells, Treg: regulatory T cells.