EXPRESSION OF TAP1 BY HUMAN TROPHOBLAST

Successful placentation in the human is dependent on the trophoblast e vading recognition and destruction by the maternal immune system. Howe ver, invasive cytotrophoblast express HLA-G which may be able to prese nt peptide to T cells. Transporter proteins are essential for peptide presentation and major histocompatibility complex (MHC) class I assemb ly. We have determined their expression by trophoblast in relation to HLA-G, using immunohistochemistry. Antitransporter protein antibody (T AP1) labeling closely paralleled that of MHC class I, but the intensit y of its expression was much greater on the HLA-G(+) extravillous cyto trophoblast than any other fetal or maternal tissue in the first trime ster and at term. This suggests that the extravillous cytotrophoblast are very actively assembling MHC class I antigens with peptides. Howev er, expression of MHC class I by the cytotrophoblast was not correspon dingly elevated. This pattern could result from HLA-G being shed from the surface of the trophoblast, a process which may play a central rol e in protecting the fetus from maternal immune attack.