Polysaccharide structure and immunological relationships of RG-I pectin from the bee pollen of Nelumbo nucifera

From the bee pollen of Nelumbo nucifera, we used hot water extraction and chromatographic fractionation on DEAE-cellulose and Sepharose CL-6B to purify polysaccharides (WNPP) to homogeneity. WNPP-2-RG (3.8 × 105 Da) consisted primarily of Rha (11.5%), GalA (12.0%), Gal (41.2%) and Ara (29.7%). Structure analysis showed that this polysaccharide is a RG-I type pectin containing AG-I and AG-II side chains comprised of 1,5-L-Ara (25.6%), t-D-Gal (12.0%), and 1,6-D-Gal (18.3%) as the primary linkage types. Immunological activity assays demonstrated that WNPP-2-RG increased lymphocyte proliferation and macrophage phagocytosis, and induced production of NO. Compared to WNPP-2-RG, its hydrolysates (RG-8H-P) had no effect on lymphocyte proliferation, although they did promote macrophage phagocytosis and decreased NO production. Our results suggest that Gal side chain residues may play a crucial role in macrophage phagocytosis, whereas Ara is unimportant for NO production and neither Gal nor Ara impact lymphocyte proliferation.