Measurement of human and mouse interleukin 18.

IL-18, originally designated as interferon-gamma (IFN-gamma)-inducing factor (IGIF), is a pleiotropic cytokine secreted by activated macrophages and Kupffer cells. The major activity associated with this cytokine is induction of IFN-gamma production from T cells, B cells, and NK cells, especially in collaboration with IL-12. IL-18 is synthesized without a signal peptide and must be enzymatically cleaved to become active. Therefore, it is important to determine whether the produced IL-18 is an active or precursor form. This unit describes functional assays for measurement of bioactive human and mouse IL-18 and ELISAs for measurement of murine and human IL-18 proteins. The functional assays are based on the induction of IFN-gamma production by IL-18. The ELISA measures the concentration of human or mouse IL-18. Using a combination of monoclonal antibodies against human or mouse IL-18, the proform and/or mature form of IL-18 can be detected by ELISA.