ABSTRACT
IL-17A is a pro-inflammatroy cytokine secreted by activated T cells. The IL-17 family consist of IL-17A, IL-17B, IL-17C, IL-17D, IL-17E and IL-17F. IL-17A and IL-17F are produced primarily in activated T cells. In contrast, IL-17B, IL-17C, IL-17D and IL-17E are expressed in a wide assortment of tissues. Their functions partially overlap those of IL-17A, although they have not been as thoroughly investigated. The receptor for IL-17A (IL-17R) is widely expressed in a variety of tissues. IL-17A and IL-17E mRNAs were expressed in only EL4 cells. IL-17C mRNA expression was observed in the thymic subcapsular/cortex epithelial cells (SNEC), cortex or cortical reticular cells (CREC), medullary epithelial cells (MEC), medullary interdigitating-like cells (MDC), thymocytes and EL4 cells. However, IL-17C mRNA was not expressed in RAW 264.7 cells. Immunohistochemical study also demonstrated not only the presence of IL-17A mainly in the thymic epithelial cells, but also the upregulated expression of IL-17A in the thymic epithelial cells of the regenerating thymus. Thus, the results of the present study suggest that IL-17A expressed in the thymocytes and thymic epithelial cells could play an important role in the development of new T cells to replace T cells damaged by cyclophosphamide treatment during thymus regeneration.