Soluble HLA-G in human placentas:: Synthesis in trophoblasts and interferon-γ-activated macrophages but not placental fibroblasts

HLA class Ib antigen, HLA-G, is highly expressed in early gestation placentas where it is believed co modulate maternal-fecal immunological interactions. In this study, soluble isoforms (sHLA-G) encoded by intron 4-retaining transcripts were identified in first trimester placentas by immunohistochemistry using a mAb specific for the C-terminus of sHLA-G. Immunoreactive sHLA-G protein was localized to trophoblast: cells and to villous mesenchymal cells with the morphological features of macrophages. Reverse transcriptase polymerase chain reaction analysis which used primers specific for intron 4 and the 3' untranslated region of the HLA-G gene showed that transcripts encoding sHLA-G were present in the trophoblast-derived Jeg-3 cells as well as interferon-gamma-activated myelomonocytic U937 cells bur were absent and uninducible in placental fibroblasts. These results indicate that placental sHLA-G is synthesized in trophoblast cells and activated placental macrophages and support the postulate that placenta-derived sHLA-G modulates maternal and fetal immune cell functions during pregnancy. Human Immunology 59, 435-442 (1998), (C) American Society for Histocompatibility and Immunogenetics, 1998. Published by Elsevier Science Inc.