Why Does Mothers Immune System Not Reject Fetus During Pregnancy: Miracle of Acceptance!!!!

The main work of the immune system of our body is to keep us safe from the invasion of foreign materials. So our body recognizes our body’s antigen as “self” and others from outside as “non-self “and by doing this the body decides to respond or not to respond to a specific antigen source.

So have u ever wondered why the fetus being a foreign body is never rejected by mothers’ immune system??? Fetus and placenta both are foreign antigens and in pregnancy, they come in direct contact with the mother’s immune system but does not have any kind of response which rejects it as seen in various kind of transplants. It’s a kind of miracle that describes the special relationship between mother and child. But yes, it does have scientific evidence too.

Let us just try to understand when the embryo is formed by the fusion of Sperm and oocyte it gets attached to women’s uterus by different phases of Implantation: Apposition, Adhesion & Penetration during these phases there are a lot of chemical changes that occur between the outer layer of fetal cells and the cells of the uterus. So during this process of the baby getting attached to the uterus, there is a various mechanism proposed by which mother and the fetus prevent the immunological reaction between them. 

It is said that the mother’s immune response becomes suppressed during this time as there is a decrease in CD4 & CD8 T-cells during pregnancy which becomes normal in the postpartum period. The mother’s immune response also shifts to immune-mediated response (Th2) rather than cell-mediated immune response (Th1). Interferons and leukocyte levels are also reduced during this phase.

There is another Hypothesis that says that there are changes in the mother’s immune system leading it to tolerate the fetus as a foreign body. The mother tolerates the antigens produced by the fetus. There is also a decrease in natural killer cell production and T cell-mediated response to Major histocompatibility responses which are produced by graft. The most important thing is fetus does not come in direct contact with the mother’s immune system and is shielded by trophoblast of the placenta. The placenta comes in contact with the mother’s immune system through two locations through syncytiotrophoblast & cytotrophoblast. These sites again prevent MHC gene production and also HLA gene A&B which are actually responsible for graft rejection. Chemo kine productions are also reduced. 

Basically, the pregnant uterus decidua is like an area where there is no immunological activity. But yes, sometimes inappropriate regulations lead to preterm labor, Abortion, Pregnancy induces Hypertension, etc. 

One other hypothesis tells that fetal antigen is suppressed and prevents its detection by the mother’s immune system. The trophoblast suppresses T-cell, B-cell & NK cell proliferation, Fasl Pathway responsible for autoimmunity is also disrupted. 

Soo there is much explanation to the mother’s acceptance of baby but still, there are many scientific mysteries that need to be unfolded with further research!!