Kinetic parameters of cell-mediated cytotoxicity (CMC) to the 13762A rat mammary adenocarcinoma were studied by using immune syngeneic (Fischer) and allogeneic (Wistar Furth) spleen cells. Treating the spleen cells with rabbit anti-T cell serum and complement eliminated cytotoxicity. Both types of cytolytic cells bound to tumor cells in Ca2+-free medium but required Ca2+ to lyse them. Cytochalasin A did not interfere with the lysis of target cells already bound to cytolytic cells but it did prevent attachment of cytolytic cells to new targets. Cytolysis of the tumor occurred in three sequential steps: 1) binding of the lymphocytes to the target; 2) production of a lytic lesion in the target by the lymphocyte; and 3) lysis of the target. Allogeneic and in vitro augmented syngeneic lymphocytes required about 30 min for maximum binding to targets compared to 4 hr for syngeneic cells sensitized in vivo. Induction of the lytic lesion required 1 hr for the allogeneic cells and up to 8 hr for both types of sensitized syngeneic cells. Target cell death was slightly faster after incubation with allogeneic (8 hr) than with syngeneic (12 hr) cells. Pretreatment of the tumor cells with mitomycin C or actinomycin D did not enhance target lysis. Despite the many similarities between allogeneic and syngeneic effector cells, the increased time required for induction of the lytic lesion by syngeneic effector cells might indicate employment of a different lytic mechanism or a lower lytic efficiency compared to allogeneic cells.

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