Two forms of interleukin-1, designated IL-1alpha and IL-1beta, have been described. Although encoded by distinct genes and exhibiting roughly only 25% sequence identity, IL-1alpha and IL-1beta bind to the same receptor and seem to elicit similar biological responses. IL-1 production is generally thought to be associated with inflammation, but it has also been shown to be expressed during kidney development, thymocyte differentiation and cartilage degradation. IL-1 plays a critical role in the regulation of immune response and inflammation, acting as an activator of T and B lymphocytes and natural killer (NK) cells.