Tumor necrosis factor-alpha: central regulatory cytokine in the induction of macrophage antimicrobial activities.

Expression of activated macrophage resistance to infection requires the cooperative interaction of interferon-gamma (IFN-gamma) and either interleukin-2 (IL-2), interleukin-4 or granulocyte/macrophage-colony-stimulating factor: no single cytokine is effective. For IFN-gamma and IL-2, the effector activity can be suppressed by the presence of anti-tumor necrosis factor-alpha (TNF-alpha) antibodies in the reaction mixture. IFN-gamma and IL-2, only in combination, induce TNF-alpha-specific mRNA and secretion of this cytokine by macrophages. Development of intracellular killing activity by activated macrophages also requires the autocrine effects of TNF-alpha. IFN-gamma provides the first signal for the production of nitric oxide (NO), the effector molecule for intracellular destruction of parasites. When IFN-gamma-treated cells are infected with pathogens, they are stimulated to make TNF-alpha. Expression of intracellular killing, as well as production of NO, is inhibited by anti-TNF-alpha antibody.