ENDOTOXIN LEVEL <0.1 EU per 1 μg of the protein by the LAL method. Human Recombinant GMP Grade IL-18 (Interleukin-18). Interleukin-18 (IL-18) is a cytokine that belongs to the IL-1 superfamily and is produced by macrophages and other cells. IL-18 works by binding to the IL-18 receptor, and together with IL-12 that it induces 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 or type II interferon that plays an important role in activating the macrophages or other cells. The combination of this cytokine and IL-12 has been shown to inhibit IL-4 dependent IgE and IgG1 production, and enhance IgG2a production in B cells. IL-18 binding protein (IL-18BP) can specifically interact with this cytokine, and thus negatively regulate its biological activity.