Study of HLA-G genotypes in preeclampsia in relation to its mRNA expression in placental tissue

Abstract

Pregnancy represents interesting phenomena not only in obstetrics and gynecology but also in the context of immunology. A central question in the immunology of pregnancy is how the fetal–placental unit avoids maternal immune rejection. Placental function contributes to the success of pregnancy in many recognized ways, such as their unusual expression of HLA class I proteins (class Ib). The lack of HLA class Ia and class II expression on trophoblasts could explain why the maternal T cells do not recognize trophoblasts as non self antigens.

HLA-G, one of class Ib genes, have a biological significance beyond its concepts on feto–maternal immune regulation. In successful pregnancy, HLA-G molecules inhibit NK cytotoxicity on the trophoblast cells. Although, HLA-G is almost monomorphic, few polymorphisms were reported. Low HLA-G expression was apparent in some of pregnancy complications as PE.

Preeclampsia (PE) is one of the leading complications in pregnancy, affecting between 2–7% of all population births. It is a progressive multisystem disorder that is unique to pregnant women. It is characterized by hypertension, edema, and proteinuria but the mode of presentation and rate of progression of the disease are extremely variable and if PE is not treated early, it may progress to eclampsia or epileptic like fits. PE is the leading cause of maternal mortality in developed countries and is associated with a five folds increase in perinatal mortality. PE is mostly confined to first pregnancies, and indeed the risk of PE in a second pregnancy is significantly reduced if the first pregnancy was normotensive. Although the symptoms of PE only become apparent in the third trimester of pregnancy, it is generally accepted that the underlying pathologic changes occur much earlier in the placenta and placental bed. Despite considerable research on preeclampsia, no obvious cause is known. The only treatment at present is removal of the fetus and placenta.