Pretreatment with Glucocorticoids Enhances T-Cell Effector Function: Possible Implication for Immune Rebound Accompanying Glucocorticoid Withdrawal

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Abstract
Glucocorticoids (GCs) exert their immunosuppressive/antiproliferative effects largely through inhibition of cytokine expression, and paradoxically upregulate the expression of (proinflammatory) cytokine receptors on select nonlymphoid cells. Clinically, withdrawal of GCs was frequently associated with worsening of the outcome of heightened immunity disorders, thereby implicating enhanced cytokine and cytokine receptor expression as a possible consequence of acute/short-term GCs withdrawal. In view of the significance of this complication of GC therapy, we addressed the effect of GC withdrawal on cytokine receptor expression and subsequent T-cell effector function, using the proliferation of human T cells as biological readout. To mimic GC withdrawal, T cells were treated with GCs or controls, stimulated, and incubated for 16–20 h at 37°C, washed, and reactivated for a further 4–48 h. Surface marker expression was assessed by FACS analysis, and proliferation was determined by measuring the cellular uptake of tritiated thymidine. Dexamethasone (DEX) and prednisolone (PRED), in a concentration-dependent manner, inhibited T-cell proliferation induced by anti-CD28 Ab + PMA. However, pretreatment of T cells activated with mitogens, cross-linking antibodies, or PMA + ionomycin (“CD3-bypass” stimulation regimen), but not resting T cells, with DEX or PRED resulted in a marked increase in IL-1R, IL-2Rα, and IL-6R expression, which was accompanied by a significant enhancement in T-cell proliferation. This effect of GCs was neither stimulus specific nor did it result from alteration in cell viability, and was paralleled by augmentation in cytokine (rIL-2) effects on DEX-pretreated and preactivated T cells. Taken together, our results underline the dual effects of GCs in regulating T-cell activation and cytokine expression. In essence, GCs directly inhibited T-cell proliferation by suppressing cytokine production, and, by enhancing cytokine receptor expression, pretreatment with GCs augmented T-cell proliferation.