Role of macrophages in tumour immunity. 3. Co-operation between macrophages and lymphoid factors in an in vitro allograft situation.

Normal mouse peritoneal macrophages were rendered cytotoxic towards target cells by incubation with immune C57B1 spleen cells taken early (7 days) and late (21 days) after a single injection of allogeneic DBA/2 lymphoma cells (L5178Y). This process, termed arming, was shown to be immunologically specific. X-irradiation of late immune spleen cells reduced their arming potential, but not that of early cells. Late immune spleen cells only were found to release spontaneously a factor which rendered macrophages weakly cytotoxic , and this release was not affected by irradiation. Both early and late immune spleen cells could be stimulated to release an arming factor by incubating them with irradiated lymphoma cells and this factor rendered macrophages strongly cytotoxic. Allo-immune serum also armed normal macrophages. Peritoneal macrophages harvested at 7 and 21 days from immunized mice were strongly cytotoxic towards the target cells. The results suggest pathways by which macrophages might become specifically cytotoxic and also integrated into the general immune response seen during rejection of the allogeneic L5178Y lymphoma.