Immunologic rejection of diethylnitrosamine-induced hepatomas in strain 2 guinea pigs: participation of basophilic leukocytes and macrophage aggregates.

The morphologic events associated with the immunologic rejection by strain 2 guinea pigs of ascites variants of two lines of diethylnitrosamine-induced tumors have been studied by light and electron microscopy. Tumor injection sites in the skin of control animals exhibited clusters of viable, actively mitotic tumor cells along with a modest inflammatory infiltrate composed of lymphocytes, macrophages, neutrophils, and rare basophils. In contrast, similar injections of either tumor line in specifically sensitized guinea pigs elicited typical delayed-type skin reactions associated with tumor cell necrosis and a more extensive inflammatory infiltrate including a selective increase in the number of basophilic leukocytes (12%, line 1, or 23%, line 10, of total inflammatory cells). That basophils may have a role in tumor resistance in vivo is suggested by the close anatomic associations observed between basophils and tumor cells, and by the fact that basophils were the only inflammatory cell to demonstrate a relative increase in frequency in the lesions of sensitized as compared with control animals. Moreover, intraperitoneal injection of line 1 tumor in specifically sensitized animals elicited a striking basophilia within 24 h. Unlike macrophages, basophils did not phagocytose tumor cells but did evidence occasional extrusion of granules and frequently exhibited loss of granule staining density, a change that may be related to release of mediator substances. Electron microscope studies of line 1 tumor rejection in the peritoneal cavities of specifically sensitized guinea pigs demonstrated aggregations of "activated" macrophages, lymphocytes, basophils, and damaged or dead tumor cells. These aggregates, held together by complex interdigitations of macrophage villi, closely resembled those occurring in vitro among peritoneal exudate cells whose migration from capillary tubes was inhibited by migration inhibition factor (MIF). Moreover, cells in these aggregates, as well as macrophages inhibited by MIF in vitro, lacked a normal coating of cell surface material.