Hawthorn Fruit (Crataegus spp.) Polysaccharides Exhibit Immunomodulatory Activity on Macrophages via TLR4/NF-κB Signaling Activation

The immunostimulatory effects and the involved molecular mechanisms of polysaccharides from hawthorn fruit (Crataegus spp.) have not been well understood. In this study, the chemical composition, monosaccharide composition, uronic acid content, and structural features of hawthorn fruit polysaccharides (HFP) and the two collected fractions were analyzed. Both AF1-2 and AF2 have pectic-like structural features rich in galacturonic acid. AF2 showed superior proinflammatory effects on macrophages which significantly increased the secretion of pro-inflammatory cytokines interleukin-1 beta, interleukin-6, and tumor necrosis factor-alpha, but not AF1-2. AF2 was found to activate the nuclear factor-kappa B signaling pathway with suppressed expression of I kappa B alpha but up-regulated expression of p-I kappa B alpha and nuclear factor-kappa B P65. The surface binding site of AF2 on macrophage cells was characterized and toll like receptor-4 was responsible for AF2 induced activation of down-stream nuclear factor-kappa B signaling pathways. AF2 from hawthorn fruit could be potentially used as a natural source of immunomodulator in functional foods.