DIFFERENTIATION OF HUMAN TROPHOBLAST POPULATIONS INVOLVES ALTERATIONSIN CYTOKERATIN PATTERNS

Cytokeratins (CKs) are related to proliferation and differentiation of epithelial cells, Little knowledge exists about CK patterns in human trophoblast subpopulations (villous and extravillous trophoblasts). To better understand differentiation and function of trophoblast compone nts, we studied the distribution patterns of CKs in the placenta throu ghout pregnancy, A panel of well-defined monoclonal antibodies against different types of cytokeratins, vimentin, and fibrin, was used on fr ozen and paraffin sections, CK8, 18, and 19 were expressed in all the villous and extravillous trophoblastic subsets throughout pregnancy. I n the first trimester, syncytiotrophoblasts were positive for CK7 and 13 along the basal membrane, As pregnancy progressed there was an incr ease in intensity of the reaction product and a more diffuse positive staining of CK7 in the cytoplasm of the syncytium, with evident positi vity along the apical membrane, CK13 showed similar expression as CK7, but with less intense staining along the apical membrane and less pro minent staining in the cytoplasm, Villous cytotrophoblasts were also p ositive for CK7 and CK13, CK17 was found related to cytotrophoblastic cells in contact with or next to Fibrin deposits, Extravillous cytotro phoblasts in cell islands and cell columns were positive for CK13 only in the cell layers located proximal to the villous stroma, whereas th e distal and more differentiated cells were negative, CK7 was positive in all epithelial cells of cell islands and columns, but the reaction product was not present in cells deeply migrated into the decidua, Am nion was negative for anti-CK13 antibodies in the first trimester but was positive at term, CK4 and CK16 were not found in the placenta, Our study shows for the first time that the different populations of huma n placental trophoblast express cytokeratins in developmental, differe ntiative, and functional specific patterns, These findings can be usef ul to distinguish and classify the various trophoblastic populations a nd provide a foundation for studying pathological aspects of the troph oblast.