Inflammatory cells in solid murine neoplasms. III. Cytotoxicity mediated in vitro by macrophages recovered from disaggregated regressing Moloney sarcomas.

Macrophages (Mphi) were recovered from disaggregated, spontaneously regressing Moloney sarcomas for in vitro testing of their cytotoxic capabilities. At a 3:1 ratio, Mphi in monolayers efficiently killed (51Cr release) a variety of tumor target cells without regard to antigenic specificity. Within 24 hr most of their cytolytic potential was lost. Killing could be restored, however, if Mphi were replated at higher cell densities. A soluble, heat-stable, dialyzable inhibitor of thymidine incorporation, which did not interfere with cellular proliferation, also was produced by Mphi recovered from Moloney sarcomas. The finding of such a competitive inhibitor, probably cold thymidine, in supernatants further opened to question the validity of radioisotope incorporation into DNA as a measure of Mphi-mediated cytostasis. The data presented suggest that Mphi may participate in the regression process by directly killing tumor cells, thus complementing the antigen-specific cytolytic capabilities of the T lymphocytes that are also found in large numbers within regressing Moloney sarcomas.