Description:
<jats:p>PROBLEM: The expression of the non‐classical HLA‐G gene has been shown at the protein level on trophoblast‐derived embryonic tissue, like the extravillous cytotrophoblast. However, the presence of HLA‐G on embryoblast‐derived cells is currently controversial. The amnion epithelium is an embryoblast‐derived cell layer covering the amnion cavity and is the main source for the amnion fluid.</jats:p><jats:p>METHOD: The expression of HLA class I molecules was investigated by immunohistochemical, biochemical, and molecular biological methods in amnion membranes and amnion fluid.</jats:p><jats:p>RESULTS: Immunohistochemically, HLA‐C and occasionally also ‐B molecules as well as HLA‐A and/or ‐G molecules have been identified on amnion 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 detected in amnion epithelial cells. Furthermore, classical HLA molecules as well as HLA‐G were found in amnion fluid.</jats:p><jats:p>CONCLUSION: These results show that the amnion epithelium frequently expresses classical HLA class I molecules as well as HLA‐G. The expression of HLA‐G antigens on amnion epithelial cells and their presence in the amnion fluid, which is continually ingested by the fetus, may be particularly relevant for the induction of peripheral tolerance.</jats:p>