Caspase-1, or Interleukin-1b (IL-1b ) Converting Enzyme (ICE), was identified as a cysteine protease that cleaves the inactive 33 kDa IL-1b precursor (proIL-1b ) into active mature 17 kDa IL-1b (Black, 1988; Kostura et al., 1989). IL-1b is a pleiotropic cytokine that is produced during inflammation, injury, immunological challenge or infection (Dinarello and Wolff, 1993; Dinarello, 1994). Only two, caspase-1 as well as caspase-3, and not caspase-2,-6,-7,-11,-12 were able to process proIL-1b to biologically active IL-1b (Van de Craen et al., 1997).

Interferon-g -inducing factor (IGIF, interleukin-18) is a recently described cytokine that shares structural features with the interleukin-1 (IL-1) family of proteins and functional properties with IL-12. Like IL-12, IGIF is a potent inducer of interferon (IFN)-g from T cells and natural killer cells. IGIF is synthesised as a biologically inactive precursor molecule (proIGIF). Since the cellular production of IL-1b , requires cleavage of its precursor (proIL-1b ) at an Asp-X site by caspase- 1, the Asp-X sequence suggested a putative processing site in proIGIF. It was demonstrated that caspase-1 processes both proIGIF and proIL-1b with equivalent efficiencies in vitro. A selective caspase-1 inhibitor blocks both lipopolysaccharide-induced IL-1b and IFN-g production from human mononuclear cells. Furthermore, caspase-1-deficient mice are defective in lipopolysaccharide-induced IFN-g production (Ghayur et al., 1997).