Immunomodulatory effects of flavonoids in vitro

Flavonoids, a group of very popular phytochemicals, exhibit numerous biological activities. We investigated immunomodulatory effects of 16 flavonoids (eriodictyol, rhamnetin, isorhamnetin, sakuranetin, isosakuranetin, pinocembrin-7-methylether, kaempferide, tamarixetin, tectochrysin, flavone, flavanone, quercetin, myricetin, morin, kaempferol and apigenin) in vitro (using cell culture models) by measuring the production of cytokines (TNFα, IL-1β, IL-2) that play crucial roles in innate and adaptive immune responses. The inhibitory effects of chosen flavonoids (30, 10 and 3µM) on IL-2 production by Jurkat cells (a cell line derived from human T-cell leukemia) stimulated with polymyristate-acetate and phytohemaglutinine was determined after 24 hrs using ELISA. The level of IL-2 produced by stimulated cells was considered as a maximal (100%), while un-stimulated cells do not produce IL-2. TNFα and IL-1β production by differentiated THP-1 cells (human macrophage-like cells) was measured using ELISA 24 hrs after the addition of flavonoids (E. coli lipopolysacharide was used as a positive control; all other reagents were LPS-free). To investigate the effects of tested compounds on cell proliferation, [6-H³] thymidine incorporation was determined. Flavonoids that significantly (>50%) inhibited IL-2 production suppressed the proliferation of Jurkat cells as well, except sakuranetin (SKN) and pinocembrin-7-methylether (P7ME). When applied even in the highest concentration these compounds did not affect Jurkat cell proliferation, but inhibited IL-2 production for 68.3% and 76.5%. All flavonoids that induced TNFα and IL-1β production for ≥50% of the positive control significantly inhibited proliferation of differentiated THP-1 cells. Interestingly, SKN and P7ME did not stimulate cytokine production, but suppressed the cell proliferation. Although all tested flavonoids exhibited immunomodulatory effects the most intriguing compounds for further investigation are SKN and P7ME.