MURINE SPLENIC MACROPHAGE TUMORICIDAL ACTIVATION BY CYTOKINES

Interleukin-2 (IL-2), IL-1 beta, interferon-gamma (IFN-gamma), and tum or necrosis factor-alpha (TNF-alpha), each alone and in all possible c ombinations, were studied for their capacity to activate murine reside nt splenic macrophages to a tumoricidal state. Two approaches were use d in these studies. The first approach was to add cytokine directly to the adherent macrophages that had been washed free of nonadherent spl een cells. The only agent effective alone was IL-2, inducing significa nt tumoricidal activity in macrophages obtained after culturing whole spleen cell suspensions for 4, but not 1 to 3, days. Nonadherent splen ic populations were required during this 4-day macrophage ''culture co nditioning.'' Only combinations of cytokines containing IL-2 were effe ctive, but none more than IL-2 alone. The second approach was to add c ytokine to the whole spleen cell suspensions for an activation period before isolation of adherent macrophages. Again, the only agent effect ive alone was IL-2. Macrophage tumoricidal activity was highest when I L-2 was added to the whole spleen cell suspensions at the initiation o f the 4-day activation culture. In addition, TNF-alpha, but none of th e other cytokines, significantly augmented the IL-2-induced effect. Th e tumoricidal activity was not a consequence of lipopolysaccharide con tamination or of lymphokine-activated killer cells. Based on the utili zation of neutralizing antibodies, IL-1 alpha, IL-1 beta, and IFN-gamm a were not involved as soluble mediators during the activation of tumo ricidal splenic macrophages by IL-2 with or without TNF-alpha.