EXPRESSION OF HLA CLASS-I MOLECULES IN HUMAN FIRST TRIMESTER AND TERMPLACENTA TROPHOBLAST

Expression of HLA class I molecules in trophoblast cells from various locations in normal human first trimester and term placenta was invest igated by immunohistochemistry with a panel of monoclonal antibodies a gainst the heavy chains or complete HLA class I molecules complexed wi th beta-microglobulin. These reagents were also employed to distinguis h between the products of different HLA class I loci. In addition to p re viously characterized reagents, a novel monoclonal antibody against HLA-A molecules (TU155) was used. Various choriocarcinoma and transfe cted cell lines served as controls for the specificities of the monocl onal antibodies. Cells in close contact with maternal cells, such as i nvading trophoblast cells and cells of the basal plate, expressed beta (2)-m micro globulin in association with HLA-G and HLA-C heavy chains. These class I heavy chains may also have been present as isolated mol ecules, although not in each of the cells. In contrast, cells of the c horion laeve exclusively expressed HLA-G, and not HLA-A, -B, or -C ant igens. Our data support the often discussed immune protective function and the regulatory function of the HLA-G molecule, during invasion. I n addition. by using monoclonal antibodies HCA2 (anti-HLA-A and -G), H C10 (anti-HLA-B and -C), TU149 (anti-HLA-B, -C, and some -A alleles), SFR8-B6 (anti-HLA-Bw6 and some -C), LA45 (some HLA-A and -B), TU48 (an ti-HLA-Bw4 and some -A), and TU155 (anti-HLA-A), we show the presence of HLA-C molecules in all extravillous trophoblast cells of the cell c olumns and in the basal plate the trophoblast cells of the chorion lae ve lack this antigen. The function of this molecule is not clear, alth ough a protective function against natural killer cell activity in the endometrium is postulated.