IL21R and thymus atrophy: IL-21, produced by TECs, can not only enhance thymic function in young and aged mice primarily by its action on double-positive thymocytes, which express high levels of IL-21 receptor after glucocorticoid-induced thymic atrophy, but also facilitate thymic regeneration and the reconstitution of the peripheral T-cell compartment in different models of thymus damage, including glucocorticoid-induced thymic atrophy, aging, and hematopoietic stem cell transplantation [53].