Children's immunology, what can we learn from animal studies (1): Decidual cells induce specific immune system of...

In mammals, pregnancy has very interesting interaction between the maternal uterus and the fetus. For maternal immune system, fetus is recognized as semiallograft. However the maternal immune cells do not attack and reject a fetus during a pregnant period. The reason why that immune tolerance is established in the maternal decidua is the specific area defined as the feto-maternal interface. While, if maternal immune cells recognize fetus as the not-self, the maternal immune cells will try to reject fetus, and then abortion will occur. For example, in a human, one of the reasons why the habitual abortion is understood as the failure of the maternal immune system. The extravillous cytotrophoblast are not attacked by the maternal immune cells, although that trophoblasts might reach even the myometrium. Exceeding the maternal myometrium doesn't decide the invasion of extravillous cytotrophoblast on the other hand. This suggests that proliferation in decidua be strictly adjusted. In human and mice, the maternal immune cells recognize the fetus trophoblasts. To escape from attack of lymphocytes, villous trophoblasts do not express classical major histocompatibility complex (MHC) class I molecules. But, in a human, extravillous trophoblasts express MHC-class I molecules such as human leukocyte antigen (HLA)-C, HLA-E and HLA-G, which are specific ligands for uterine NK (uNK) cells. In the decidua, various lymphocytes including T-cells, Tregs, macrophages, and uNK cells exist. Each immunocytes are not identified on their function, compose network with the decidual cells under progesterone existence, and interact with the success of pregnancy.