Fig. 2

At pregnancy day 5 in rats, maternal innate and cellular immune cells cannot cross the placental barrier into the fetus to provide protection. Therefore, in order to prevent fetal abortion, the cellular immune activity mediated by maternal Th1 is inhibited, thus enhancing humoral immunity. The aim is to activate B cells to produce large amounts of IgG, which cross the placental barrier into the fetus through FcγRn and provide protection, i.e. Th1 transformation into Th2 occurs. At pregnancy day 7, the fetal heart is fully developed, and the embryo has its own circulatory system; at this time, FcγRn bound maternal IgG in the fetus exchange with FcγRs on the surface of innate immune cells in the fetus. In order to activate fetal innate immune cells, transformation of Th2 into Th1 is completed in the maternal immune system, so that the embryo uses maternal IgG to mediate its innate immune protection and to provide protection for itself. (Some of the pictures in this figure are from Roopenian DC [8])