Characteristics of xenograft. II. Cytostatic effector mechanism for xenograft rejection

Cytolytic activity was detected by the 51 Cr-release test with Concanavalin A (Con A)-stimulated rat lymphocytes, when peritoneal exudate (PE) cells were obtained from mice immunized by intraperitoneal injection of rat lymphocytes. Such PE cells did not exert cytolytic activity on rat tumor cells. When mice were immunized with mitomycin C-treated rat tumor cells, their PE cells exerted low or negligible degrees of cytolytic activity on both types of target cells. When cytostatic activity was assayed by inhibition of the incorporation of 125 IUDR into rat tumor cells, the activity was detected in the whole PE cells of mice immunized with rat lymphocytes or tumor cells but not in their spleen or glass-nonadherent PE cells. Mouse tumor cells were also sensitive to the cytostatic activity of such a cell population. Normal AKR PE cells became cytostatic to rat tumor cells, when they were exposed to the supernatants prepared from the culture containing immune PE cells and antigens. The supernatants alone did not exert cytostatic activity.