AMNION EPITHELIAL-CELLS, IN CONTRAST TO TROPHOBLAST CELLS, EXPRESS ALL CLASSICAL HLA CLASS-I MOLECULES TOGETHER WITH HLA-G

PROBLEM: The expression of the non-classical HLA-G gene has been shown at the protein level on trophoblast-derived embryonic tissue, like th e extravillous cytotrophoblast. However, the presence of HLA-G on embr yoblast-derived cells is currently controversial. The amnion epitheliu m is an embryoblast-derived cell layer covering the amnion cavity and is the main source for the amnion fluid.METHOD: The expression of HLA class I molecules was investigated by immunohistochemical, biochemical , and molecular biological methods in amnion membranes and amnion flui d. RESULTS: Immunohistochemically, HLA-C and occasionally also -B mole cules as well as HLA-A and/or -G molecules have been identified on amn ion epithelial cells. These results were extended by Western blotting with purified amnion epithelial cells where HLA-B and/or -C, HLA-A and HLA-G antigens have been detected. As expected HLA-G mRNA was detecte d in amnion epithelial cells. Furthermore, classical HLA molecules as well as HLA-G were found in amnion fluid. CONCLUSION: These results sh ow that the amnion epithelium frequently expresses classical HLA class I molecules as well as HLA-G. The expression of HLA-G antigens on amn ion epithelial cells and their presence in the amnion fluid, which is continually ingested by the fetus, may be particularly relevant for th e induction of peripheral tolerance.