Interleukin-18 (IL-18) is a proinflammatory cytokine produced by macrophages and other cells that belongs to the IL-1 superfamily. IL-18 works together with IL-12 to induce cell-mediated immunity following infection with microbial products like lipopolysaccharide (LPS). After stimulation with IL-18, natural killer (NK) cells and certain T cells release another important cytokine called interferon-gamma (IFN-gamma) or type II interferon that plays an important role in activating macrophages or other cells.
Apart from its physiological role, interleukin-18 is also able to induce severe inflammatory reactions, which suggests its role in certain inflammatory disorders. This proinflammatory cytokine can induce the IFN-gamma production of T cells, and the combination of this cytokine and IL-12 has been shown to inhibit IL-4 dependent IgE and IgG1 production and to enhance IgG2a production of B cells.