Pregnancy is a special condition in which the woman's immune system must activate a tolerance mechanism so as not to reject the baby's body during the entire gestation period. To do this, the embryo expresses the HLA G antigen, whose function is to suppress the cells of the mother's immune system and that there is no rejection.
However, there are cases in which there is a failure in the mechanism of tolerance, so that the mother's immune system does not recognize the embryo as its own and, therefore, rejects it causing an abortion. This usually occurs in women who have a high number of Natural Killer (NK) cells, immune system cells that destroy embryonic tissues by not recognizing them.
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