Immunohistochemistry of tertiary villi (human placenta, midpregnancy )

Stain: Immunoperoxidase staining with diaminobenzidin (DAB) and hematoxylin counterstaining for keratin 7 (OVTL 12-30 antibody) at the left (A) and for human anti-chorionic gonadotrophin (hCG-DAKO 231antibody) at the right (B). Tertiary villi show a keratin-positive reaction (brown-stained) in all postmitotic multinucleated syncytiotrophoblast cells (STC, 1). Notice the brushborders along the whole surface of these lining cells. (4) indicates the intervillous space. Single row of weakly keratin-positive cytotrophoblast cells (CTCs or Langhans cells, 2) which closely adhere to the STC. The loosely arranged embryonic connective tissue (3) is negative for keratin 7. Both epithelial cell types are connected by desmosomes (see electron microscopy pictures). The right photograph (B) shows the exclusive positive staining for hCG in the cytoplasm of the STC (1). The CTCs (2) are negative and are likely not 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. Semi-free floating cells (leukocytes) and cell debris are negative.