FIG. 2.
Phase contrast microscopy of the cell cultures. a, Initial isolates consist largely of “organoid” clusters of cells (inset) which after 24 h begin to spread over the plate. b, After 8 to 12 d the plates become confluent with a cobblestone appearance. c, The cells begin to form spheres containing debris after 3 to 4 wk (bottom arrow). Note the smaller polygonal cells in the top center of c and the nearby multinucleated cell (top arrow). Immunoperoxidase staining for prekeratin reveals that virtually all cells are positive (d) showing crisscrossing fibrils in the cytoplasm (inset).