Polysaccharide fraction isolated from Korean Saccharina japonica alleviates impaired immune responses in macrophages and immunosuppressed mice

This research aimed to investigate the immunostimulating properties of polysaccharides extracted from Saccharina japonica (SJP). Initially, the SJP was a heteropolysaccharide composed of seven different monosaccharides, such as fucose, galactose, mannose, glucuronic acid, guluronic acid, and mannuronic acid. The SJP stimulated the release of NO, IL-6, and TNF-α and mRNA expression of macrophage. Furthermore, these outcomes were closely associated with immunostimulatory signaling pathways including MAPK and NF-κB. Additionally, immunostimulation by SJP is caused by various pattern recognition receptors including dectin-1, SR, and CD14. Prophylactic administration of SJP effectively prevented the toxicity of cyclophosphamide on body weight and the spleen index. In addition, SJP improved the function of various splenic immunocytes such as natural killer cells, CD4 + , CD8 + , CD11b + , and CD45R + cells. Especially, the improvement effects on serum IL-6, TNF-α, IgA, and IgG were notable. These results suggest that polysaccharides isolated from S. japonica have high potential as immunomodulators. • SJP isolated from Saccharina japonica is a mixture of alginate and fucoidan. • SJP activated the immune response of macrophages. • Macrophage activation by SJP is deeply related to MAPK, NF-κB, and several PRRs. • The immune response suppressed by cyclophosphamide was mitigated by SJP.