Polysaccharides from lichen Xanthoria parietina: 1,4/1,6-α-D-glucans and a highly branched galactomannan with macrophage stimulating activity via Dectin-2 activation

Hot-water soluble polysaccharides H-1-3 and H-2-1 were isolated from the thalli of the lichen Xanthoria parietina (L) Th. Fr. and purified by ion exchange and gel permeation chromatography. Structure elucidation was mainly based on 2D-NMR and nano-ESI-Q-TOF MS/MS experiments. H-1-3 (13.7 kDa) was shown to be linear a-glucan with alpha-D-Glcp-(1 -> [->[4)-alpha-D-Glcp-(1](2)->[6)-alpha-D-Glcp-(1](3 ->) 4)](n) core backbone. The (1,4)- and (1,6)-alpha-D-Glcp linkages were in a 2:3 M ratio. H-2-1 (525 kDa) was characterized as a complex branched beta-galacto-alpha-mannan with -> [6)-alpha-D-Manp-(1 -> [2,6)-alpha-D-Manp-(1](2) ->[2)-alpha-D-Manp-(1](2)->](n) core units and main side chains of (1,3)-(beta-D-Galf linked at 0-6 to -> 2)-alpha-D-Manp-(1 ->, together with minor terminal units of 1,4/1,6-alpha-D-Glcp units attached to the core chain at 0-6 position and alpha-L-Rhap linked to Galf side chain at 0-2 position (Manp: Calf: Glcp: Rhap linkage ratio = 9:3:2:1). H-2-1 exerted strong immunoactivity in vitro and activated murine RAW macrophages 264.7 towards significantly increased phagocytosis, TNF-alpha and IL-beta secretion. These effects are due to an interaction of the galactomannan with the transmembrane pattern-recognition protein Dectin-2 of the macrophages. (C) 2019 Elsevier B.V. All rights reserved.