Role of macrophages in tumour immunity. II. Involvement of a macrophage cytophilic factor during syngeneic tumour growth inhibition

Abstract

Growth inhibition by immune or armed macrophages of target L5178Y or SL2 (DBA/2) lymphoma cells leading to their death required an immunologically specific cell-to-cell contact, and was not mediated via a soluble product of the macrophages. The lymphoma cells were not irreversibly damaged if left in contact for up to 24 hours with the immune macrophages and grew normally when removed, but while in contact there was little or no growth of the cells. Immune macrophages progressively lost their cytotoxic capacity after prolonged exposure to the target cells. The antigenic recognition of specific lymphoma cells by immune macrophages could be blocked by the presence of allo-immune serum directed against the lymphoma cells, but this was not affected by treatment of the macrophage monolayers with rabbit anti-mouse γ-globulin, and only slightly affected by high concentrations of trypsin. The involvement of cytophilic factors during the cytotoxic reaction is discussed in relation to the presence of γ-globulin or non-immunoglobulin factors on immune macrophage membranes and after the arming of non-immune macrophages by contact with hyperimmune spleen cells or with SMAF (the specific macrophage-arming factor) found in supernatants of mixed cell cultures of sensitized lymphoid cells and specific lymphoma cells.