Immunostimulatory Polysaccharide Fractionated from a Liquid Culture by Phellinus linteus Mycelium

A liquid culture was fermented using Phellinus linteus mycelium, and 5 fractions were isolated to evaluate the possibility of using them as postbiotic ingredients. The fractions isolated were: Hot-water extract (PL-HW) from whole liquid culture, crude polysaccharide (PL-CP) from PL-HW by ethanol (EtOH) precipitation, hot-water extract (PM-HW) from isolated mycelia, crude polysaccharide (PM-CP) from PM-HW, and exopolysaccharide (EPS) from culture supernatant by EtOH precipitation. Innate immunostimulating activity using the RAW 264.7 cell line showed that EPS induced the most effective production of tumor necrosis factor-alpha (TNF-α), monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6), and nitric oxide. In addition, adaptive immunostimulating activity using splenocytes isolated from C3H/HeN mice revealed that PL-HW, PM-HW, and EPS induced prominent splenocyte proliferation. Specifically, EPS stimulated the production of Th1-activated cytokines such as TNF-α and interferon-gamma (IFN-γ) in splenocytes, suggesting its effectiveness in cell-mediated adaptive immune activation. General chemical analysis showed that the immunostimulatory EPS was composed of neutral sugar (90.2%), uronic acid (6.1%), protein (1.2%), and polyphenols (2.5%). Component sugar analysis indicated that EPS was composed of a high proportion of glucose (94.9%), and small amounts of mannose (3.8%), galactose (0.9%), and glucuronic acid (0.4%). In conclusion, it was confirmed that glucan-type exopolysaccharide fractionated from the culture supernatant of the P. linteus mycelium can promote both innate and adaptive immune cell stimulation.