Antagonistic and synergistic effects of glucocorticoids and IL-7 on CD4+ T cell activation

Glucocorticoids (GCs) are steroidal compounds widely used to treat chronic and acute inflammatory diseases. In particular, GCs at pharmacological doses induce apoptosis of activated and naïve T cells, inhibit their proliferation and block pro-inflammatory cytokine secretion. At physiological concentrations, the effect of these steroids on T cell immunity are not yet fully understood, and various studies reported paradoxical roles exerted by GCs on T cell immunity. Here, we show that GCs surprisingly induce proliferation of activated CD4+ T cells in the presence of IL-7, a cytokine secreted in the thymus and at mucosal sites. Increased proliferation is dependent on a GC-mediated survival of mitotic cells. Moreover, we observe a downmodulation of Th1 cytokine secretion in cells treated with GCs, an outcome which is not affected by the presence of IL-7. GCs exert thus a positive role in the presence of IL-7 by enhancing proliferation of CD4+ T cells and simultaneously a negative role by suppressing pro-inflammatory cytokine production.