Immunohistochemical staining of placenta with mAb 57B to MAGE-A4. Segmental reactivity in week 32 placenta with immunopositive and immunonegative (*) areas separated by septum (arrows). Abbreviations: BP, basal plate; CP, chorionic plate. (A) Higher magnification of placental septum of placenta with intense immunopositivity of septal extravillous trophoblast facing immunopositive villous area and mostly negative extravillous trophoblast cells of septum (arrows) facing immunonegative (*) area (B). (C) Homogeneously stained area in a week 8 placenta. Focal staining of villous (D) and extravillous (E) trophoblast of the basal plate; villi in a week 37 placenta with focal immunopositive structures in villous stroma consisting mostly of endothelial cells (arrows) revealing nuclear staining (F).