An electron microscope study of histiocyte response to ascites tumor homografts.

When the ascites forms of the DBA/2 lymphoma L1210 or the C57BL E.L. 4 lymphoma are injected into C3H mice, host histiocytes (macrophages) accumulate and are responsible for the destruction of a large number of tumor cells. Many of the tumor cells, often apparently intact, are ingested. The ingestion process is rapid and depends upon invagination of an area of the histiocyte with simultaneous projection of cytoplasmic fimbriae which complete the encirclement. The earliest change seen in the enclosed cell is shrinkage; digestion of the cell wall and cytoplasmic elements fol lows. Phagocytosis accounts for only a proportion of the cells destroyed by histiocytes. Other cells are probably destroyed when their cell membrane is broken down in an area in contact with a histiocyte, apparently permitting fusion of the two cytoplasms.