Identification of PR-positive cell types at the fetal-maternal interface. (Panel a) Low power image of fetal membranes showing the immunohistochemical staining patterns obtained with antibodies that detect all isoforms of PR (clone 1A6) and (C-20), antibodies that detects only PR-B (San27) and antibodies that detect only PR-A (clone 16). An equivalent amount of mouse immunoglobulins (IgG) or antibody pre-adsorbed with immunising peptide (BP), against which C-20 antibodies were generated, indicates specificity. Immunoreactivity is indicated with the black arrows in the amniotic (a), the star in the chorionic (c) and with red arrows in the decidual (d) layers of the fetal membranes. (Panel b) The presence of cytoplasmic PR and an absence of PR-B and PR-A isoforms are demonstrated in term amnion epithelial cells (1, 4, 7, and 10), and chorionic cytotrophoblasts (2, 5, 8, and 11). Both cytoplasmic and strong nuclear staining was observed in the decidua (3, 6, 9 and 12) indicating the presence of cytoplasmic and nuclear PR isoforms. Bar = 50 μm; Data are representative of six independent samples.