Platelets are localized around the endovascular trophoblasts within the maternal vessels. Sections of placental tissue from therapeutic hysterectomy at 9 weeks of gestation were double stained with rhodamine (red) and FITC (green). (E-G) Higher magnifications of the boxed area indicated in panel A. (A) H&E staining. (B) CD41 (platelet marker, red) and cytokeratin 7 (CK7, marker for trophoblasts and endometrial gland, green). (C) CD41 (red) and von Willebrand factor (VWF, endothelial marker, green). (D) CD45 (leukocyte marker, red) and VWF (green). (E) CD41 (red) and CK7 (green). (F) Collagen type IV (COL IV, red) and CK7 (green). (G) Fibronectin (FN, red) and CK7 (green). TB, trophoblasts. Platelets were confined within the maternal blood vessel (C). These platelets were attached to the vessel wall (dotted white lines), which was infiltrated by spindle-shaped perivascular trophoblasts (E) or adhered to the surface of round endovascular trophoblasts (E), where collagen type IV and fibronectin were deposited (F-G). Endometrial sections from nonpregnant women in the secretory phase (postovulatory day 7) were also double stained by CD45 and CD41 (red; H and I, respectively) and VWF (green). CD45⁺ immune cells were distributed around spiral arteries, but no platelets were observed within the spiral arteries. Scale bars indicate 100 μm. Original magnification × 120 (panels A-D), × 320 (panels E-G), and × 200 (panels H and I).