A polysaccharide fraction from Achillea millefolium increases cytokine secretion and reduces activation of Akt, ERK and NF-κB in THP-1 monocytes

•A polysaccharide, Am-25-d, was isolated from Achillea millefolium.•Am-25-d increased LPS-induced cytokine secretion by THP-1 monocytes.•Am-25-d decreased LPS-induced phosphorylation/activation of Akt, ERK1/2 and NF-κB.•Am-25-d may be of use as an immunoenhancer.

Achillea millefolium has been used in traditional medicine for a number of ailments, including skin inflammation and wounds. A polysaccharide fraction (Am-25-d) isolated from aqueous extract from A. millefolium had an average molecular weight of 270 kDa and a monosaccharide composition of GalA, Gal, Ara, Xyl, Rha in molar ratio of 28:26:23:9:7. THP-1 cells primed with IFN-γ and stimulated with LPS in the presence of Am-25-d secreted more IL-1β, IL-8, IL-10, IL-12p40, IL-23 and TNF-α than THP-1 cells stimulated in the absence of Am-25-d. However, when added to unstimulated cells Am-25-d did not increase secretion of the cytokines examined. Stimulating THP-1 monocytes in the presence of Am-25-d led to decreased nuclear concentrations of NF-κB and phosphorylation of ERK1/2 and Akt kinases compared with that when the cells were stimulated without Am-25-d. These findings indicate that Am-25-d isolated from A. millefolium has immunoenhancing properties that may be mediated via the Akt pathway.