Microcinematographic and electron microscopic study of the death of human tumor cells induced by histiocytic cells.

The cells from a malignant fibrous histiocytoma were enzymatically isolated and cultured in vitro. The cultures were observed by microcinematography and with an electron microscope after fixation and embedding. The interactions between histiocytic and tumor cells resulted in tumor cell death. The microcinematographic study revealed that filiform projections of the histiocytic cell protrude toward the tumor cell surface making contacts for varying periods of time. The tumor cell then contracts and almost simultaneously some granules (lysosomes?) appear in the tumor cell cytoplasm. These granules eventually fuse with each other thus increasing in volume. The resulting granulation heads for the periphery of the tumor cell at a site previously touch by a projection of a histiocytic cell; at this site the membrane bursts and the tumor cell dies leaking amorphous cytoplasmic material. Before bursting the tumor cell does not show any noticeable morphological changes.