Also known as interferon-gamma-inducing factor (IGIF) and IL-1γ, IL18 is a cytokine that bears structural similarities with members of the IL-1 family of proteins. IL18 is natively synthesized as a proform that gets processed by caspase-1 to generate the bioactive form of IL18. IL18 is one of the pro-inflammatory cytokines that is expressed by a variety of immune and non-immune cells. The activities of IL18 appear to be species specific. An important function of IL18 is the regulation of functionally distinct subsets of T-helper cells required for cell mediated immune responses. IL18 functions as a growth and differentiation factor for Th1 cells and is known to up-regulate the FAS ligand mediated cytotoxic activity of murine natural killer cells. IL18 also partakes in a complex regulatory circuit involved in causing cell death by apoptosis.