Interleukin-22 (IL-22) is a protein that in humans is encoded by the IL22gene.[5][6]
Structure
IL-22 is an α-helical cytokine. IL-22 binds to a heterodimeric cell surface receptor composed of IL-10R2 and IL-22R1 subunits.[7] IL-22R is expressed on tissue cells, and it is absent on immune cells.[8]
Crystallization is possible if the N-linked glycosylation sites are removed in mutants of IL-22 bound with high-affinity cell-surface receptor sIL-22R1. The crystallographic asymmetric unit contained two IL-22-sIL-22R1 complexes.[7]
IL-22 biological activity is initiated by binding to a cell-surface complex composed of IL-22R1 and IL-10R2 receptor chains and further regulated by interactions with a soluble binding protein, IL-22BP, which shares sequence similarity with an extracellular region of IL-22R1 (sIL-22R1). IL-22 and IL-10 receptor chains play a role in cellular targeting and signal transduction to selectively initiate and regulate immune responses.[7] IL-22 can contribute to immune disease through the stimulation of inflammatory responses, S100s and defensins. IL-22 also promotes hepatocyte survival in the liver and epithelial cells in the lung and gut similar to IL-10.[11] In some contexts, the pro-inflammatory versus tissue-protective functions of IL-22 are regulated by the often co-expressed cytokine IL-17A [12]
IL-22 is a member of a group of cytokines called the IL-10 family or IL-10 superfamily (including IL-19, IL-20, IL-24, and IL-26),[13] a class of potent mediators of cellular inflammatory responses. It shares use of IL-10R2 in cell signaling with other members of this family, IL-10, IL-26, IL-28A/B and IL-29.[14]
IL-22, signals through the interferon receptor-related proteins CRF2-4 and IL-22R.[6] It forms cell surface complexes with IL-22R1 and IL-10R2 chains resulting in signal transduction through receptor, IL-10R2. The IL-22/IL-22R1/IL-10R2 complex activates intracellular kinases (JAK1, Tyk2, and MAP kinases) and transcription factors, especially STAT3. It can induce IL-20 and IL-24 signaling when IL-22R1 pairs with IL-20R2.
Regulation of production
IL-22 production is induced mainly through IL-23 receptor signalling. IL-23 is produced by dendritic cells after recognition of ligands by specific Toll-like receptors especially in combination with Dectin-1 and or NOD2 signalling. IL-1β stimulates IL-22 production too. On the other hand IL-22 binding protein is a soluble inhibitor which blocks receptor binding site of IL-22.[9]
^Moore KW, de Waal Malefyt R, Coffman RL, O'Garra A (2001). "Interleukin-10 and the interleukin-10 receptor". Annual Review of Immunology. 19: 683–765. doi:10.1146/annurev.immunol.19.1.683. PMID11244051..
Wong CK, Lun SW, Ko FW, Wong PT, Hu SQ, Chan IH, et al. (2009). "Activation of peripheral Th17 lymphocytes in patients with asthma". Immunological Investigations. 38 (7): 652–64. doi:10.1080/08820130903062756. PMID19811428. S2CID36646289.
Pan HF, Zhao XF, Yuan H, Zhang WH, Li XP, Wang GH, et al. (March 2009). "Decreased serum IL-22 levels in patients with systemic lupus erythematosus". Clinica Chimica Acta; International Journal of Clinical Chemistry. 401 (1–2): 179–80. doi:10.1016/j.cca.2008.11.009. PMID19046958.