Tumor cell interactions in vitro microtubules, 100 angstrom filaments, and contractile microfilaments of tumor cells involved in "emperipolesis".

An increase in the number of examples of emperiopolesis, i.e., cells within cells, was observed subsequently to addition of Bt2cAMP to spinner flask cultures of JB-1-E tumor cells. A conspicuous arrangement of microtubules and 100 angstrom filaments in the tumor cells involved in emperiopelesis was observed. Absence of emperipolesis in cultures treated with cytochalasin B indecates a possible role of the contractile microfilaments in the events leading to emperiopolesis. The significance of and the term emperipolesis are discussed.