Interleukin-18 (IL-18) has been identified as a molecule that induces IFN-gamma production and enhances NK cell cytotoxicity. IL-18 receptor (IL-18R) is a type I membrane protein present in lung, leukocytes, spleen, liver, thymus, prostate, small intestine, colon, placenta and heart, and absent from brain, skeletal muscle, pancreas and kidney. IL-18R is present in Hodgkins disease cell lines, and does not bind IL-1alpha or IL-1beta. The association of IL-18 to IL-18R leads to activation of NFkappaB. At present two subunits of IL-18R have been characterized: IL-18Ralpha and IL-18Rbeta. IL-18Ralpha has been described as the ligand-binding chain and IL-18Rbeta as the signal-transduction chain.
