Immunological Function of HLA-G Exepressed on trophoblasts.

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To understand the basic relationship of HLA class I to maternal-placental immune tolerance, we have attempted to dissect the expression of soluble (S) HLA-G from menbrance bound (M) HLA-G and to investigate the expression of other nonclassical class I,specifically HLA-E.Towards this goal, we have developed a set of HLA-G specific monoclonal antibodies which allow the distinction of the soluble and membrane G1 proteins, and have used these and specific anti-HLA-E reagents in immunohisto-chemical staining to localize these three proteins in placental tissue. Further, we used HLA-G specific antibodies to isolate S・HLA-G and M・HLA-G directly from placental tissue in order to examine bound peptides.1. Expression of HLA-G and HLA-EImmunohistochemical staining of placenta demonstrated that S・HLA-G was found expressed in syncyciotrophoblasts, cytotrophoblasts, and extravillous cytotrophoblasts and was also apparent in maternal blood at intervillous space. Consistent with previous reports, M・HLA-G was found expressed only in extravillous cytotrophoblasts. HLA-E was expressed weakly in synciciotrophoblasts and cytotrophoblasts and comparatively more strongly in extravillous cytotrophoblasts, essentially in parallel with total HLA-G.2. Antigen presenting ability of HLA-GTo investigate the ability, TAP dependency of HLA-G expression, and sequence of HLA-G bound peptide were examined. When HLA-G was isolated from transfected cells, a relatively large number of bound peptides derived from intra cellular proteins were identified, but the number of bound peptides was considerably smaller and the individual abundance considerably higher, with a single peptide species accounting for 15% of the total peptide bound to HLA-G from the placenta.