Regulatory mechanisms of IL-2 and IFN gamma suppression by quercetin in T helper cells

Abstract

Quercetin is a popular flavonoid compound that is biosynthesized by plants; it is suggested to modulate a variety of inflammatory responses of macrophages and T lymphocytes. Oral administration of quercetin in arthritic rats dramatically diminishes clinical signs of arthritis. Moreover, quercetin ameliorates experimental autoimmune encephalomyelitis, which is associated with Th1-mediated immune responses. Like quercetin inhibits macrophage-induced cytokine production, it also blocks IL-12-dependent JAK-STAT signaling in Th cells. Despite the anti-inflammatory effects of quercetin acting through Th cells, the regulatory mechanisms remain unclear. Here, we studied the function of quercetin in Th cells and found that quercetin suppressed both IFN gamma and IL-2 production upon T cell receptor stimulation. Furthermore, we uncovered the regulatory mechanisms of quercetin involved in the inhibition of cytokine production during Th cell activation. The fact that quercetin-derived IFN gamma suppression was blocked in T-bet-deficient Th cells demonstrated quercetin act through the modulation of T-bet expression. Whereas IL-2 inhibition by quercetin was independent of T-bet expression, quercetin diminished IL-2R alpha expression, which is critical for positive regulatory loop of IL-2 autoactivation. Taken together, quercetin is suggested to repress both IFN gamma and IL-2 cytokine production by independent mechanisms; T-bet-dependent IFN gamma suppression and IL-2R alpha-dependent IL-2 inhibition. (c) 2008 Elsevier Inc. All rights reserved.