Formononetin, a phyto‐oestrogen, and its metabolites up‐regulate interleukin‐4 production in activated T cells via increased AP‐1 DNA binding activity

Summary Phyto‐oestrogens are polyphenolic non‐steroidal plant compounds with oestrogen‐like biological activity. Phyto‐oestrogens have many biological effects including oestrogen agonist/antagonist properties. However, the effect of phyto‐oestrogens on allergic responses remains unclear. In this study we investigated whether formononetin, a phyto‐oestrogen, and its metabolites, daidzein and equol, affect production of interleukin‐4 (IL‐4), a pro‐inflammatory cytokine closely associated with allergic immune response, in primary CD4+ T cells and EL4 T lymphoma cells. Formononetin, daidzein and equol significantly enhanced IL‐4 production from both CD4+ T cells and EL4 cells in a dose‐dependent manner. Formononetin, daidzein and equol also enhanced IL‐4 gene promoter activity in EL4 cells transiently transfected with IL‐4 gene promoter constructs, but this effect was impaired in EL4 cells transfected with an IL‐4 promoter construct deleted of P4 site carrying nuclear factor of activated T cells (NF‐AT) and activator protein‐1 (AP‐1) binding sites. In addition, formononetin, daidzein and equol increased AP‐1 DNA binding activities while did not affect NF‐AT DNA binding activities. The enhancing effects on IL‐4 production and AP‐1 DNA binding activities were abrogated by specific inhibitors for phosphatidylinositol‐3‐kinase (PI3K), protein kinase C (PKC) and p38 mitogen‐activated protein kinase (MAPK), indicating that formononetin, daidzein and equol might enhance IL‐4 production by increased activation of AP‐1 through the PI3‐K/PKC/p38 MAPK signalling pathway. These results suggest that phyto‐oestrogens and some of their metabolites may increase allergic responses via the enhancement of IL‐4 production in T cells.