Signaling pathway and structural features of macrophage-activating pectic polysaccharide from Korean citrus, Cheongkyool peels

To characterize the immuno-stimulating ingredient from the Korean citrus, Cheongkyool, a crude polysaccharide (CCE-0) was isolated from the pectinase digests of Cheongkyool peels, from which the complex polysaccharide CCE-I was purified to homogeneity by gel filtration. CCE-I highly enhanced the production of IL-6, TNF-alpha, and NO in RAW 264.7 cell lines. It augmented the mRNA expression of IL-6, TNF-alpha, and iNOS in a dose-dependent manner. Moreover, CCE-I dose-dependently induced phosphorylation of MAPK5 and NF-kappa B related proteins and led to the nuclear translocation of p65. The effect of CCE-I on NO and IL-6 production was suppressed by treatment with specific antibodies for TLR2, TLR4, and scavenger receptors. Conversely, the primary structure of CCE-I that exhibited potent immunostimulatory activity was characterized by sugar composition, linkage analysis, and oligosaccharide analysis after beta-elimination. The results suggested that CCE-I may be a rhamnogalacturonan-I type, highly branched polysaccharide with short arabinan and galactan side chains. (C) 2019 Elsevier B.V. All rights reserved.