Immunohistochemical detection of ERα in MCF-7 cells and human placenta at term. A proportion of MCF-7 breast carcinoma cells show strong nuclear staining with h-151 [A] and ID5 antibodies [B]. [C] No staining of MCF-7 is apparent with control (CD3) antibody recognizing human T lymphocytes. [D] In normal placentae, cytotrophoblast cells (c) associated with trophoblastic syncytium (s) show strong nuclear staining with ID5 antibody (used for all placental samples stained for the ERα), which decreases in cytotrophoblast cells entering the syncytium [E]. [F] CD3 control shows an isolated T cell but no staining of other villous structures. Vascular ERα immunoreactivity is not associated with the nuclei of endothelial cells (black arrows, G and H). However vascular pericytes (PC and white arrow, H) are strongly stained. [I] In abnormal placentae, the ERα immunoreactivity was associated with villous vasculature only. [J] Staining of villous fibroblasts persisting after vascular regression. Fibroblasts beneath the amniotic epithelium show ERα staining [K], but no ERα immunoreactivity is apparent in the amniotic epithelium [L], extravillous trophoblast (EVT) [M] and decidual cells [N]. [O] Strong Thy-1 staining of decidual cells (right) and no staining of EVT (left).