Cytokines are considered vital mediators of the immune system. Down- or upregulation of these mediators is linked to several inflammatory and pathologic situations. IL-26 is referred to as an identified member of the IL-10 family and IL-20 subfamily. Due to having a unique cationic structure, IL-26 exerts diverse functions in several diseases. Since IL-26 is mainly secreted from Th17, it is primarily considered a pro-inflammatory cytokine. Upon binding to its receptor complex (IL-10R1/IL-20R2), IL-26 activates multiple signaling mediators, especially STAT1/STAT3. In cancer, IL-26 induces IL-22-producing cells, which consequently decreases cytotoxic T cell functions and promotes tumor growth through activating anti-apoptotic proteins. In hypersensitivity conditions such as rheumatoid arthritis, multiple sclerosis, psoriasis, and allergic disease, this cytokine functions primarily as the disease-promoting mediator and might be considered a biomarker for disease prognosis. Although IL-26 exerts anti-microbial function in infections such as hepatitis, tuberculosis, and leprosy, it has also been shown that IL-26 might be involved in the pathogenesis and exacerbation of sepsis. Besides, the involvement of IL-26 has been confirmed in other conditions, including graft versus host disease and chronic obstructive pulmonary disease. Therefore, due to the multifarious function of this cytokine, it is proposed that the underlying mechanism regarding IL-26 function should be elucidated. Collectively, it is hoped that the examination of IL-26 in several contexts might be promising in predicting disease prognosis and might introduce novel approaches in the treatment of various diseases.
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