Abnormal T helper 17 (Th17) responses promote inflammation and cause inflammatory diseases. Natural components that modulate Th17 functions can be effective for the amelioration of inflammatory diseases. Procyanidin B2 3,3''-di-O-gallate (PCB2DG) contained in grape seeds markedly suppressed interleukin (IL)-17 production from spleen cells but not CD4⁺ T cells. The aim of this study was to elucidate the mechanisms by which PCB2DG suppresses IL-17. Our results showed that PCB2DG suppressed the production of IL-17, tumor necrosis factor (TNF)-α, IL-1β, and IL-6 with the suppression of transcription factors expression. In addition, we revealed that TNF-α and IL-1β were required to induce IL-17 production in this experimental condition, and PCB2DG suppressed these cytokines from dendritic cells (DCs). Furthermore, CD4-DC co-culture experiments showed that the production of IL-17, TNF-α, and IL-1β was markedly inhibited in co-cultures of PCB2DG-pretreated CD4⁺ T cells and DCs. These results suggested that PCB2DG first modulated TNF-α production by CD4⁺ T cells and then suppressed IL-1β secretion from DCs, resulting in decreased IL-17 production. Thus, PCB2DG can control the cytokine network associated with Th17 cells, providing a novel mechanism underlying the immunosuppressive effects of polyphenols.

Procyanidin B2 3,3''-di-O-gallate (PCB2DG), one of dietary polyphenol, markedly suppressed interleukin (IL)-17 production. The inhibitory effect on IL-17 production was mediated by cytokine induction from both CD4⁺ T cells and dendritic cells (DCs). PCB2DG first modulated tumor necrosis factor-α production by CD4⁺ T cells and then suppressed IL-1β secretion from DCs, resulting in decreased IL-17 production. Thus, PCB2DG can control the cytokine network associated with Th17 cells.