Study on the immunomodulatory activity of a novel polysaccharide from the lichen Umbilicaria Esculenta

Umbilicaria esculenta possesses nutritional properties, such as antioxidant, antithrombotic and lipid peroxidation inhibitory activity. The immune effects of its polysaccharide (Umbilicaria esculenta polysaccharide, UEP) on murine macrophages RAW264.7 were investigated for the first time. UEP promoted their proliferation and phagocytic activity obviously. At the concentration of 600 μg mL^-1, UEP stimulated their proliferation and phagocytosis to 1.4 and 2.5 times, respectively, as compared with the negative group. Moreover, UEP induced their release of nitric oxide (NO), NO synthase (NOS), tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ) and interleukin factors (IL-1β, IL-6 and IL-10) in a concentration-dependent manner. The production of NO and NOS was increased to 25.2 and 2.7 times, respectively, while the secretion of those cytokines was enhanced to multiples from 1.9 to 2.6 times. At the same time, TAK242, an inhibitor of TLR4 (Toll-like receptor 4), inhibited UEP influences on these factors with inhibition rates up to 50%, which indicated that UEP acted on murine macrophages mainly via TLR4. UEP has positive immunomodulatory functions in murine macrophages, and can be developed as a potential novel immunomodulator.