Results from animal and In vitro studies have produced contradictory results suggesting both an induction and inhibition of Th1 cytokines (Muthian & Bright 2004, Nairetal 2002).
According to in vitro data quercetin induces Th1 -derived cytokines (promoting cellular immunity) and inhibits Th2-derived cytokines, which exert negative effects on cellular immunity (Nair et al 2002). An excess of Th2 cytokines has also been implicated in allergic tendencies, which provides a theoretical basis for the use of quercetin as an anti-allergic substance. Conversely animal studies have demonstrated that quercetin is able to inhibit Th1 differentiation and signalling of IL-12 (Muthian & Bright 2004). As this occurred in the presence of a Th1 cell-mediated inflammatory demyelinating autoimmune disease model of multiple sclerosis suggestive of Th1 excess, a possibility exists that quercetin actually exerts an immunomodulatory effect on these cells. Further trials are required to elucidate the exact effects of quercetin under different conditions.
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