IL4 and abortion: IFN-γ, IL4, IL13 and other cytokines secreted by Th1 and Th2 cells interact with each other to maintain maternal immune tolerance to the fetus and ensure fetal growth and development during pregnancy, while Th1 cells oversecrete IFN-γ, which can damage trophoblast cells by inducing activated NK cells, hindering embryo implantation and placental growth and development, and thus lead to abortion.25