Tumor-basophil interactions in vitro--a scanning and transmission electron microscopic study.

Purified guinea pig basophils, or basophils either specifically degranulated with antigen or nonspecifically degranulated with lectin, were cultured with guinea pig line 1 hepatoma cells for 1 to 24 hr and studied ultrastructurally. As early as 1 hr of culture, degranulated or nongranulated basophils and tumor cells formed close contacts by mutually intertwined elongated cell processes and also in cultures containing degranulated basophils, extruded membrane-free basophil cytoplasmic granules became firmly attached to tumor cells. At later intervals, some tumor cells cultured with basophils exhibited cytostatic and cytopathic changes, including dense mitochondria, centralization of organelles, dilated perinuclear and rough endoplasmic cisternae, cell swelling and cytoplasmic lucency, disrupted cytoplasmic organelle and plasma membranes, nuclear pyknosis and fragmentation. Some tumor cell specialized surface attachments were either disrupted or damaged at points of basophil or basophil granule adhesion. Tumor damage was most extensive in cultures containing degranulated basophils, although only a minority of tumor cells (less than 10%) was affected. Tumor injury was seen much less frequently in the presence of nondegranulated basophils, and was absent in control cultures of tumor alone. The occasional viable tumor cells that phagocytosed basophil granules were apparently unharmed, suggesting that internalization of basophil granules by tumor cells is not cytotoxic.