PLACENTAL EXPRESSION OF HLA CLASS-I GENES

This article presents an overview of the more recent data dealing with the constitutive, transcriptional, and translational expression of cl assical class Ia and nonclassical HLA-E and -G class Ib products in th e different trophoblast cell subpopulations that constitute the matern ofetal interface during human pregnancy. Of particular interest is the expression of alternatively spliced HLA-G transcriptional isoforms th at may be translated in membrane-bound or soluble protein products. Mo lecular regulatory mechanisms that may control the differential expres sion of class Ia and class Ib molecules, according to the cell types, state of differentiation, and stages of gestation are also examined. T hey may operate at the levels of transcription, translation and/or tra nsport of proteins to the cell surface. Functional significance of the absence of detectable cell surface expression of class Ia molecules i n all trophoblast cell subpopulations, and of the presence of membrane -bound HLA-G products in extravillous cytotrophoblast cells is finally questioned.