Cultured human amniotic fluid cells characterized with antibodies against intermediate filaments in indirect immunofluorescence microscopy.

Cells cultured from second trimester human amniotic fluid were characterized in indirect immunofluorescence (IIF) microscopy using specific antibodies against the subunit proteins of different types of cytoskeletal intermediate filaments. Most of the amniotic fluid cell cultures contained only epithelial cells as indicated by the positive keratin-fluorescence in IIF. Five distinct types of keratin-positive cells could be characterized. A dominating cell type (E-1) in most cultures were rapidly proliferating epithelial cells, previously called amniotic fluid cells (AF-cells). These cells showed a fibrillar cytoplasmic fluorescence both with keratin antibodies and with antibodies against vimentin, the fibroblast type of intermediate filament protein. E-1 cells did not show the typical cell-to-cell arrangement of keratin fibrils between the adjacent cells, a characteristic previously found in most cultured epithelial cells. Most of the cultures also contained large epitheloid cells (E-2), showing a fine fibrillar cytoplasmic organization of both keratin- and vimentin filaments, clearly different from that seen in E-1 cells. Several cultures contained two additional epithelial cells both showing the typical cell-to-cell arrangement of keratin fibrils (E-3 and E-4). These two cell types could be distinguished because of their distinct difference in size. E-4 cells typically grew as small cell islands among other epitheloid cells. Amniotic fluid cell cultures occasionally contained also large multinucleated cells (E-5), which appeared to contain large amount of fibrillar keratin. Fibroblastic cells, identified by their decoration only with antibodies against vimentin, were rarely found in amniotic fluid cell cultures. Interestingly, in such cultures some cells with a fibroblastoid appearance were identified as epithelial cells on the basis of the positive keratin-fluorescence. The results show the suitability of IIF with cytoskeletal antibodies in characterization of heterogenous cell populations and indicate that normal amniotic fluid cell cultures mostly contain epithelial cells.