HLA CLASS-I EXPRESSION ON THE MATERNO-FETAL INTERFACE

PROBLEM: The conditions that permit the genetically dissimilar (haplo- non-identical) human fetus to evade rejection by its mothers immune sy stem have been the subject of intense interest for several years. As t he placental cells, which are in contact with maternal blood or tissue , are devoid of HLA class II antigens, the interest has focused on the expression of HLA class I molecules. METHOD OF STUDY: Recent findings on the constitutive, transcriptional, and translational expression of HLA class I molecules on anatomically and morphologically different s ubpopulations of trophoblast cells will form the basis of this article . RESULTS: The expression of HLA class I molecules in the trophoblast cells, forming the materno-fetal junctional zone is inhomogeneous. It differs depending on the differentiation and location of trophoblast c ells within the placenta and furthermore on the stage of gestation. On the transcriptional level HLA-A, -B, -C, -E, and -G could be detected on individual trophoblast populations, whereas only HLA-C and HLA-G s eem to be translated to protein. CONCLUSIONS: The expression of HLA cl ass I antigens by trophoblast cells is not simply suppressed. Instead, less polymorphic HLA-G and HLA-C antigens are carefully selected from the class I multigene family. This gives rise to the assumption that these two HLA class I molecules play an important role in the maintena nce of pregnancy.