DISTRIBUTION OF CELLS BEARING THE HNK-1 EPITOPE IN THE HUMAN PLACENTA

HNK-1 (Leu-7 antigen or CD57) is a unique carbohydrate moiety found in certain glycosphingolipids and several cell adhesion glycoproteins on the cell membrane. Previous studies have suggested that HNK-1 carbohy drates act as adhesive ligands in cell-cell interactions. Using a mono clonal antibody reactive to the HNK-1 moiety and an immunoperoxidase m ethod on formalin-fixed paraffin-embedded tissue, the expression of th e HNK-1 epitope in human placentae was confined to the intermediate tr ophoblast (IT) in trophoblastic columns. The number of HNK-1 immunorea ctive IT cells increased from the proximal to the midportion of the tr ophoblastic column, and then disappeared at the junction of the column with the basal plate where IT infiltrates the endomyometrium and beco mes extravillous IT. Neither cytotrophoblast nor syncytiotrophoblast r eacted with the HNK-1 antibody. In hydatidiform moles, HNK-1 immunorea ctivity was localized to areas that structurally resembled trophoblast ic columns. In contrast, placental site trophoblastic tumours which do not contain structures analogous to trophoblastic columns did not exp ress HNK-1 epitope. Expression of HNK-1 was only rarely observed in ch oriocarcinomas, being present in less than 5 per cent of trophoblastic cells in two of 13 cases. The murine placenta, which lacks trophoblas tic columns, was negative for HNK-1. Thin-layer chromatography immunos taining demonstrated the HNK-1 reactive glycosphingolipids in placenta l lipid extracts, whereas Western blot analysis from placental protein extracts failed to reveal detectable glycoproteins that demonstrated I-INK-I immunoreactivity. In conclusion, the specific localization of I-INK-I reactive glycosphingolipids in trophoblastic columns of the hu man placenta suggests that the HNK-1 moiety may play an important role in maintaining cohesion between intermediate trophoblastic cells in t he trophoblastic columns thereby contributing to the structural integr ity of the villi that anchor the placenta to the basal plate. (C) 1997 W. B. Saunders Company Ltd.