Description
Interleukin 18 (IL-18), also known as interferon-gamma-inducing factor (IGIF) and IL-1r, is a cytokine which shares biologic activities with IL-12 and structural similarities with the IL-1 family of proteins. IL-18 was originally cloned from liver cells and has since been shown to be expressed by monocyte/macrophages, osteoblasts and keratinocytes. Caspase-1 (IL-1 beta-converting enzyme) has been implicated in the physiological processing of pro-IL-18 to IL-18. Similarly to IL-12, human IL-18 has been shown to enhance NK cell activity in PBMC cultures. Human IL-18 has also been found to induce the production IFN-r and GM-CSF while inhibiting the production of IL-10 by PBMC. On enriched human T cells, human IL-18 can enhance Th1 cytokine production and stimulate cell proliferation via an IL-2-dependent pathway. In the mouse system, IL-18 has been shown to be a costimulatory factor for the activation of Th1, but not Th2, cells. IL-18 was found to selectively enhance the FasL-mediated cytotoxicity of Th1, but not Th0 or Th2, cells. IL-18 has also been shown to induce activated B cells to produce IFN-r that inhibits IgE production