Ultrastructural differentiation of a clonal human embryonal carcinoma cell line in vitro.

A cloned human embryonal carcinoma (EC) cell line 2102Ep derived from a testicular teratocarcinoma was characterized by means of electron microscopy and immunohistochemistry. These EC cells when plated at high cell density grow mostly as undifferentiated cells displayed relatively little pleomorphism. Eighty-five to 90% of these cells contain keratin in the form of peridesmosomal tonofilaments. Cell populations of the same clonal line plated at a low cell density contain, in addition to undifferentiated EC cells, large cells displaying complex cytoplasmic architecture, more complex junctions, and intracytoplasmic keratin in the form of bundles. Some of these cells also react with antibodies to human chorionic gonadotropin indicative of trophoblastic differentiation. Furthermore, some cells form "morules" which are multicellular aggregates composed of a core of EC cells and an attenuated, more differentiated outer cell layer. These data thus point out not only some similarities but also even more prominent differences between human and mouse EC cells.