The interaction of activated macrophages with normal and neoplastic cells

The interaction of various cell types with Salmonella enteritidis 11RX activated macrophages was examined. P815 tumour cells, Concanavalin A-activated blast cells and splenic lymphocytes were tested for their ability to bind to activated macrophages whilst the ability to inhibit macrophage-mediated lysis of 51Cr-labelled P815 tumour cells was tested with unlabelled tumour cells and blast cells. All three cell types were bound by activated macrophages but only P815 cells were lysed by the activated macrophages and only these cells could act as cold target inhibitors of cytolysis. This phenomenon could not be explained by the release of cytotoxic factors resulting from the interaction of blast cells with activated macrophages. The lack of cold target inhibition by blast cells may have been due to the detachment of initially adherent blast cells leaving the activated macrophages free to interact with tumour cells.