Macrophage requirement for in vitro generation of specific, secondary cell‐mediated cytotoxicity against SV40‐induced tumor‐associated antigens in mice

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Abstract
The role of adherent phagocytic cells in an in vitro secondary cytotoxic response against Simian virus 40 (SV40)‐induced tumor‐associated antigens was investigated. Spleen cells (responder cells), from mice primed with syngeneic SV40‐transformed cells, extensively depleted of macrophages by filtration through a Sephadex G–10 column followed by iron carbonyl treatment, had a markedly decreased capacity to generate in vitro secondary cytotoxic reactivity against syngeneic SV 40‐transformed cells when cultured with the relevant stimulator cells. The secondary response was restored by the addition of adherent peritoneal cells from normal mice syngeneic to those immunized with the antigen. Within a certain dose range, small numbers of peritoneal cells completely reconstituted the response, whereas large numbers inhibited the reactivity. The restored cultures maintained specific cytotoxic reactivity against SV40‐induced tumor‐associated antigens which was mediated by effector T cells as shown by sensitivity to anti‐Thy‐1.2 antiserum and complement. These results suggested a requirement for adherent phagocytic cells (accessory cells) in in vitro generation of a secondary, cytotoxic response to tumor‐associated antigens.