Contributions of IL-22 to Th17 responses: Repairing and protecting peripheral tissues
IL-22 is a cytokine mainly produced by Th17 cells under the control of IL-23. Although this cytokine is structurally related to IL-10, it does not share any activity with IL-10 and is, so far, completely devoid of activity on immune and hematopoietic cells. IL-22 responsive cells are mainly found in peripheral tissues and include keratinocytes, lung and intestinal epithelial cells as well as hepatocytes. In vivo, IL-22 expression fits with the spectrum of inflammatory processes related to Th17 activation, including multiple sclerosis, inflammatory bowel disease and psoriasis in human. However, its pathophysiological significance varies in each of these diseases. IL-22 does not seem to play any major role in multiple sclerosis, at least based on the classical mouse model for this disease. By contrast, this cytokine appears to play a protective role in mucosal inflammation both in lungs and colon. Finally, IL-22 turns out to be one of the main proinflammatory mediators responsible for inappropriate activation of keratinocytes in psoriasis lesions, raising some promising perspectives for future clinical applications.
KeywordsTh17 Cell Experimental Autoimmune Encephalitis Physiol Gastrointest Liver Psoriasis Lesion Mouse Colitis Model
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