Regulation and function of interleukin-36 cytokines in homeostasis and pathological conditions.

IL-36α, IL-36β, and IL-36γ are members of the IL-1 family of cytokines that signal through a common receptor composed of IL-36R and IL-1R/AcP to activate NF-κB and MAPKs, such as p38 and JNK, and promote inflammatory responses. IL-36Ra is a natural antagonist of the 3 IL-36 agonists that binds to IL-36R and inhibits binding of the agonistic ligands. These cytokines are expressed predominantly by epithelial cells and act on a number of cells, including immune cells, epithelial cells, and fibroblasts. Processing of the N terminus is required for full agonist or antagonist activity for all IL-36 members. The role of IL-36 has been demonstrated extensively in the skin, where it can act on keratinocytes and immune cells to induce a robust inflammatory response and is implicated strongly through functional and genetic evidence in the pathology of psoriatic disorders. Emerging data also suggest a role for this cytokine family in pulmonary physiology and pathology. Although much has been learned about the biochemistry of IL-36 and its role in various tissues, it is clear that we are at an early stage in our understanding of the full biology of these cytokines.