Immunoenhancing glucuronoxylomannan from Tremella aurantialba Bandoni et Zang and its low-molecular-weight fractions by radical depolymerization: Properties, structures and effects on macrophages.

In this study, a glucuronoxylomannan named TAP-3 was obtained from high-value Tremella aurantialba Bandoni et Zang. Physicochemical analysis revealed that TAP-3, which had a molecular weight of ∼624 kDa, mainly consisted of d-mannose (Man), d-xylose (Xyl), and d-glucuronic acid (GlcA) in a molar ratio of 3.0:1.0: 1.0. Structural analyses of its depolymerized fragments clarified that TAP-3 contained a (1 → 3) and (1 → 2)-linked α-Manp backbone, side chains formed by β-Xylp and β-GlcpA linked to the C-2 position of α-Manp, and acetyl groups connected to the sixth hydroxyl positions of Manp. TAP-3 showed marked immune enhancement activity, promoting NO, IL-1β and TNF-α secretion from macrophages. The critical membrane receptor of TAP-3 was identified to be TLR4, and the chain length was essential for its immunoregulatory activity. These findings expand knowledge of the structural types of glucuronoxylomannan and illustrate its biological activity as an immunopotentiator.