IL-18 R beta/IL-1 R7: ProductsThe functional IL-18 receptor complex is composed of two subunits designated IL-18 R alpha (also termed IL-1 R5 and IL-1 Rrp) and IL-18 R beta (also termed IL-1 R7 and AcPL). Both IL-18 R alpha and IL-18 R beta belong to the IL-1 receptor family. Although IL-18 R alpha by itself binds IL-18 with low-affinity and IL-18 R beta does not bind IL-18 in vitro, co-expression of IL-18 R alpha and IL-18 R beta is required for high-affinity binding and IL-18 responsiveness. IL-18 R is widely expressed in numerous tissues including spleen, thymus, leukocyte, liver, lung, heart, small and large intestine, prostate and placenta. It is not expressed in brain, skeletal muscle, kidney and pancreas.