HLA and pregnancy problems
Cases of recurrent abortions, pre-eclampsia or babies born with hemolytic diseases of the new born raise a questiion "Why did your mother reject you?" Although, after looking at the complexity of the maternal-foetal immune interactions and the cases of successful pregnancies, with surprise and admiration to the question now becomes "Why didn't your mother reject you?" The cells from the placenta are the only part of the foetus that interacts directly with the mother's uterine cells, and therefore, the maternal immune system is able to evade immune rejection. The foetus itself has no direct contact with maternal cells. Moreover, the foetus per se is known to express paternal HLA antigens and is rejected as allograft if removed from its cocoon of trophoblast and transplanted to the tight muscle or kidney capsule of the mother. A number of mechanisms have been proposed to account for the immune-privileged state of the decidua. The different hypothesis can be summarized in the five main ideas:
- A mechanical barrier effects of the trophoblast
- Suppression of the maternal immune system during pregnancy
- The absence of HLA class I molecules in the trophoblast
- Cytokine shift and more recently
- Local immune suppression mediated by the Fas/FaL system
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