ABSTRACT
IL-18 is a newly-identified player in the turbulent world of cytokines. Originally identified as an activity present in the livers of mice primed with heat-killed Propionibacterium acnes and further challenged with lipopolysaccharide (LPS) [1], it was found to induce secretion of interferon-γ (IFNγ) by T cells and NK cells, a property which inspired the name IFN-γ-inducing factor (IGIF). Since its first description, the murine cDNA has been cloned [2], as has its human homologue [3], enabling the production of recombinant protein and a more extensive characterization of its properties. While a primary role remains the induction of IFN-γ secretion, it is now clear that the cytokine is pleiotropic: in addition to influencing both innate and adaptive arms of the immune response, IL-18 appears to perform housekeeping functions, such as the regulation of bone resorption and deposition [4]. As its sphere of influence has broadened, so its original name has proven inadequate; the proposal that it be designated IL-18 has therefore been widely endorsed.
