Influence of Short-Term Glucocorticoid Therapy on Regulatory T Cells In Vivo

Background: Pre- and early clinical studies on patients with autoimmune diseases suggested that induction of regulatory T(T-reg) cells may contribute to the immunosuppressive effects of glucocorticoids(GCs). Objective: We readdressed the influence of GC therapy on T-reg cells in immunocompetent human subjects and naive mice. Methods: Mice were treated with increasing doses of intravenous dexamethasone followed by oral taper, and T-reg cells in spleen and blood were analyzed by FACS. Sixteen patients with sudden hearing loss but without an inflammatory disease received high-dose intravenous prednisolone followed by stepwise dose reduction to low oral prednisolone. Peripheral blood T-reg cells were analyzed prior and after a 14 day GC therapy based on different markers. Results: Repeated GC administration to mice for three days dose-dependently decreased the absolute numbers of T-reg cells in blood (100 mg dexamethasone/kg body weight: 2.8 +/- 1.8 x 10(4) cells/ml vs. 33 +/- 11 x 10(4) in control mice) and spleen (dexamethasone: 2.8 +/- 1.9 x 10(5)/spleen vs. 95 +/- 22 x 10(5)/spleen in control mice), which slowly recovered after 14 days taper in spleen but not in blood. The relative frequency of FOXP3(+) T-reg cells amongst the CD4(+) T cells also decreased in a dose dependent manner with the effect being more pronounced in blood than in spleen. The suppressive capacity of T-reg cells was unaltered by GC treatment in vitro. In immunocompetent humans, GCs induced mild T cell lymphocytosis. However, it did not change the relative frequency of circulating T-reg cells in a relevant manner, although there was some variation depending on the definition of the T-reg cells (FOXP3(+): 4.0 +/- 1.5% vs 3.4 +/- 1.5% ; AITR(+): 0.660.4 vs 0.5 +/- 0.3%, CD127(low): 4.0 +/- 1.3 vs 5.0 +/- 3.0% and CTLA4+: 13.8 +/- 11.5 vs 15.6 +/- 12.5%; p < 0.05). Conclusion: Short-term GC therapy does not induce the hitherto supposed increase in circulating T-reg cell frequency, neither in immunocompetent humans nor in mice. Thus, it is questionable that the clinical efficacy of GCs is achieved by modulating T-reg cell numbers.