Expression of intermediate filaments in cultured cells.

The occurrence of different types of intermediate filaments in primary cultures of cells and in cultured cell lines was studied by the indirect immunofluorescence (IFL) technique. The antibodies used were spontaneous monoclonal human antibodies of immunoglobulin M (IgM) class against vimentin-type intermediate filaments (fibroblast 58 x 10 mol. wt subunit protein), and experimental rabbit antibodies of IgG class against vimentin, desmin (muscle 55 x io mol. wt subunit protein), glial fibrillary acidic protein (GFA), 68 x io mol. wt neurofilament polypeptide and human keratin polypeptides. Cultured fibroblasts from different species, and both aortic and venous endothelial cells, showed a fibrillar cytoplasmic fluorescence when stained with antibodies against vimentin. On the other hand, in cultures of chicken embryonal fibroblasts, cells showing a bright desminspecific fluorescence, but lacking vimentin-specific staining, were seen even after several subcultivations. The presence of both desmin and vimentin polypeptides in these cultures was also confirmed by polyacrylamide gel electrophoresis. In chicken fibroblast cultures the 2 types of intermediate filaments were not expressed simultaneously in individual cells, whereas in baby hamster kidney (BHK-21) cells and human rhabdomyosarcoma cells a variable co-staining with anti-vimentin and anti-desmin antibodies could be seen. In contrast, cultured human fibrosarcoma cells and simian virus 40-transformed human fibroblasts showed only vimentinspecific fibrillar fluorescence. Glial cells from mouse embryonic spinal cord appeared to express only GFA-containing intermediate filaments in a primary culture, whereas both subcultured mouse glial cells and a cultured glioma cell-line also showed vimentin-specific staining. On the other hand, neuronelike cells in the primary cultures could only be stained with the antibodies to 68 x io mol. wt neurofilament polypeptide. Interestingly, clones ofmouseneuroblastoma(Ci 300) cells contained