Toll-like receptor ligand-induced activation of murine DC2.4 cells is attenuated by Panax notoginseng

The medicinal herb, Panax notoginseng, has been used for thousands of years in traditional Chinese medicine and possesses anti-inflammatory properties. Dendritic cells (DCs) play a central role in the regulation of both inflammation and adaptive immunity. The aim of this study was to investigate the potential for notoginseng extracts to modulate Toll-like receptor (TLR) ligand-induced activation of cultured DC2.4 cells. Following stimulation with LPS, CpG or poly(I:C) and treatment with 0-50 μg/ml notoginseng extract for 24 h, DCs were evaluated for various phenotypic and functional readouts. Notoginseng reduced the LPS-, CpG- and poly(I:C)-induced production of TNF-α by DC2.4 cells. Also, IL-6 production by notoginseng-treated cells stimulated with LPS and CpG but not poly(I:C) was reduced when compared to controls. TLR ligand-induced CD40 expression was attenuated by notoginseng. In contrast, notoginseng decreased CD86 levels on DCs activated with LPS and poly(I:C) but not CpG. Inhibition of TNF-α production was time-dependent in LPS-stimulated cells, occurring only with pretreatment or concurrent treatment of notoginseng but not after delayed addition of the herbal extract. Additionally, ginsenoside Rg1 more effectively inhibited LPS-stimulated cytokine production by DC2.4 cells than ginsenoside Rb1. Taken together, these results demonstrate that notoginseng inhibits the production of specific inflammatory molecules and innate immune responsiveness by DCs following TLR activation.