IL-1 pathways in inflammation and human diseases

Interleukin (IL)-1 was first cloned in the 1980s, and rapidly emerged as a key player in the regulation of inflammatory processes. The term IL-1 refers to two cytokines, IL-1 alpha and IL-1 beta, which are encoded by two separate genes. The effects of IL-1 are tightly controlled by several naturally occurring inhibitors, such as IL-1 receptor antagonist (IL-1Ra), IL-1 receptor type II (IL-1RII), and other soluble receptors. Numerous IL-1 inhibitors have been developed and tested primarily in rheumatoid arthritis, with only modest effects. By contrast, the use of IL-1 antagonists has been uniformly associated with beneficial effects in patients with hereditary autoinflammatory conditions associated with excessive IL-1 signaling, such as cryopyrinopathies and IL-1Ra deficiency. Successful treatment with IL-1 blockers has also been reported in other hereditary autoinflammatory diseases, as well as in nonhereditary inflammatory diseases, such as Schnizler syndrome, systemic-onset juvenile idiopathic arthritis and adult Still disease. The role of microcrystals in the regulation of IL-1 beta processing and release has provided the rationale for the use of IL-1 inhibitors in crystal-induced arthritis. Finally, preliminary results indicating that IL-1 targeting is efficacious in type 2 diabetes and smoldering myeloma have further broadened the spectrum of IL-1-driven diseases.