IL-22 vs. IL-22: The Tissue Matters

IL-22 is a cytokine recently discovered to be produced by TH17 cells. Its receptor is expressed in the skin, liver, the digestive and the respiratory tract where IL-22 conveys signals of the immune system directly to the tissue. IL-22 is involved in the host defense against extracellular pathogens as well as in autoimmune inflammatory diseases and exerts, depending on the tissue and inflammatory context, proinflammatory, protective or no evident function. Focusing on im- mune-mediated pathology, here we will discuss the role of IL-22 in the context of tissue inflammation to provide an over- view of the complex properties of this bi-functional cytokine and to disentangle some of its apparently aberrant actions.