Eupatorium japonicum extract regulates inflammation through suppression of the TRIF-dependent signaling pathway of toll-like receptors

Inflammation can be mediated by invading microbial pathogens. Toll-like receptors (TLRs) recognize invading microbial pathogens, inducing innate immune responses. Broadly, the activation of TLRs induces two major downstream signaling pathways, myeloid differential factor 88 (MyD88)- and Toll/interleukin 1 receptor domain-containing adapter inducing interferon-β (TRIF)-dependent pathways, which lead to the activation of nuclear factor-κB (NF-κB) and interferon regulatory factor 3 (IRF3). To evaluate the therapeutic potential of the ethanol extracts of flowers of Eupatorium japonicum Thunb (EJE), its effect on signal transduction via the TLR signaling pathways induced by lipopolysaccharide (LPS) or polyinosinic-polycytidylic acid (poly[I:C]) was examined. EJE suppressed the activation of NF-κB and IRF3 induced by LPS or poly[I:C]. EJE also inhibited LPS- or poly[I:C]-induced IRF3 phosphorylation as well as interferon-inducible genes, such as interferon inducible protein-10. These results suggest that EJE can modulate TLR signaling pathways, realizing effective therapeutic options for chronic inflammatory diseases.