Tertiary villi (human placenta, early pregnancy)

Stain: (A, left) Azan. (B, right) Immunoperoxidase staining with diaminobenzidin (DAB) and hematoxylin counterstaining for human anti-chorionic gonadotrophin (hCG-DAKO 231 antibody). (A) shows blue grey-stained postmitotic multinucleated syncytiotrophoblast cells (STC, 1b), partially cut tangentially (1a). These lining cells display an extensive brush border along the whole surface. Some lysed cells are observed within the intervillous space (4).The cytotrophoblasts (2) form a single row of lightly stained cells (CTCs or Langhans cells) closely adhering to the STC, as part of the placental barrier. (3) Loose embryonic connective tissue. (B) The right picture shows that the STCs (1) exclusively are stained positively (brown) for hCG. The CTCs (2), however, remain negative and appear not to be involved in the production of hCG. Due to the DAB-reaction an enhanced staining of the population of dark-brown lysosomal granules of the STCs is obtained.