Biological or Clinical Significance:
Interleukin 18 (IL-18) is a 18kDa novel cytokine which is identified as a costimulatory factor for production of interferon-γ (IFN- γ) in response to toxic shock. It shares functional similarities with IL-12. IL-18 is synthesized as a precursor 24kDa molecule without a signal peptide and must be cleaved to produce an active molecule. IL-1 β converting enzyme (ICE, Caspase-1) cleaves pro-IL-18 at aspartic acid in the P1 position, producing the mature, bioactive peptide that is readily released from the cells. It has been reported that IL-18 is produced from Kupffer cells, activated macrophages, keratinocytes, intestinal epithelial cells, osteoblasts, adrenal cortex cells and murine diencephalon.
IFN-γ is produced by activated T and NK cells and plays critical roles in the defense against microbial pathogens. IFN- γ activates macrophages, enhances NK activity and B cell maturation, proliferation and Ig secretion, induces MHC class I and II antigens expression, and inhibits osteoclast activation.
IL-18 acts on T helper 1-type T (Th1) cells and in combination with IL-12 strongly induces production of IFN- γ by these cells. Pleiotropic effects of IL-18 have also been reported, including enhancement production of IFN- γ and GM-CSF in peripheral blood mononuclear cells, production of T helper type 1 cytokines, IL-2, GM-CSF and IFN- γ in T cells, enhancement of Fas ligand expression by T helper type 1 cells.
Principle of Test Method:
The IL-18 assay measures human IL-18 by sandwich ELISA.
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