Localization of HLA-G proteins in erythroid cells from first-trimester trophoblast by immunohistochemistry. (A) Expression of soluble HLA-G5/-G6 by cell island trophoblast (CIT) and by erythroid (ER) cells but not by perivillous trophoblast (PVT) was determined by using the 5A6G7 mAb. (B) Analysis of HLA-G5/-G6, CD34, CD71, and CD45 expression on the developing vessels present in first-trimester trophoblast tissue. (C) Immunohistochemical staining of serial trophoblast sections of a differentiated vessel from a 32-day embryo. Analysis was performed by using antibodies to HLA-G5/-G6 (5A6G7 mAb), CD34 which marks endothelial (ED) cells lining vessel, CD71 which identifies erythroid (ER) cells, and CD45 which targets both lymphoid and myeloid cells. Original magnifications: × 100 (A), × 200 (B), and × 400 (C).