Green Tea Catechin Metabolites Exert Immunoregulatory Effects on CD4⁺ T Cell and Natural Killer Cell Activities

Tea catechins, such as (-)-epigallocatechin-3-O-gallate (EGCG), have been shown to effectively enhance immune activity and prevent cancer, although the underlying mechanism is unclear. Green tea catechins are instead converted to catechin metabolites in the intestine. Here, we show that these green tea catechin metabolites enhance CD4⁺ T cell activity as well as natural killer (NK) cell activity. Our data suggest that the absence of a 4′-hydroxyl on this phenyl group (B ring) is important for the effect on immune activity. In particular, 5-(3′,5′-dihydroxyphenyl)-γ-valerolactone (EGC-M5), a major metabolite of EGCG, not only increased the activity of CD4⁺ T cells but also enhanced the cytotoxic activity of NK cells in vivo. These data suggest that EGC-M5 might show immunostimulatory activity.