Participation of three lymphoid cell types in the in vitro activation of cell-mediated immunity to a syngeneic gross virus-induced lymphoma in rats

Abstract

W/Fu rats inoculated with the syngeneic Gross-virus induced lymphoma, (C58NT)D, had transient lymphocyte-mediated specific cytotoxicity against the tumor cells at 7–15 days after tumor injection. Spleen cells 40 days after immunization (spleen 40) were unreactive by a direct 4-hr 51Cr release assay, but activity appeared after in vitro culture of these spleen eclls by themselves for 18–24 hr. The nature of the cells involved in the activation of cytotoxicity and the characteristics of the effector cells themselves were studied. Significant differences were seen in the cell types involved in the activation phase and the effector phase. Activation appeared to require the cooperation of three cell types. Induction of activity was lost by treatment of cells with ATS plus complement, by passage over an EAC-column, or by treatment with carbonyl iron. Thus, T cells, CRL and macrophages were necessary for full activation of cytotoxicity in spleen 40. In contrast, after activation, only CRL seemed to be required for cytotoxicity, and treatment wih ATS or carbonyl iron had little effect. The effector cell detected after in vitro activation was quite distinct from that seen in the direct cytotoxicity assay with spleen cells at 10 days after tumor cell inoculation. The early, direct cytotoxic reactivity was dependent on T cells, being eliminated by treatment with ATS and complement but not by EAC columns or carbonyl iron. It appears therefore that the in vitro activation is a separate mechanism for cytotoxicity against tumor cells, rather than a simple recovery of T cells from in vivo inhibition.