Extraction and molecular characterisation of polysaccharides from Suaeda maritima for their immunomodulatory effects

In the present study, Suaeda maritima polysaccharides (SMPs) were identified, characterised and evaluated for their immune-modulating effects on RAW264.7 macrophages and the underlying biological processes. Two acidic polysaccharides (SMP-F1 and SMP-F2) were obtained via ion-exchange chromatography from the crude polysaccharide (SMP-C). The SMP-C and its fractions mainly contained carbohydrates, proteins and sulphates, in variable proportions. Glucose, mannose, galactose and arabinose were the primary monosaccharide units, accompanied by smaller amounts of rhamnose and xylose. The molecular weight (Mw) of the SMPs ranged from 76.2 × 10³ to 245.0 × 10³ g/mol. SMPs can significantly induce the production of NO by up-regulating iNOS expression. The results showed that SMPs could increase TNF-α, IL-6, IL-10 and IL-12 expression. In addition, SMP-F2 significantly boosts inflammatory reactions more than SMP-C or SMP-F1. Further study revealed that SMP-F2 was found to stimulate macrophage phagocytosis and the expression of CD11b, CD14, CD40 and TLR4. The major chains of the strongest immunostimulant, SMP-F2, were mainly 1,3-linked Manp, 1,4-linked Glcp and 1,4-linked Galp. The side chain of SMP-F2 was 1,3,6-linked Manp and 1,4,6-linked Galp, with terminals of arabinose, mannose and glucose. These findings show that SMPs, particularly SMP-F2, promote the ability to modulate immunological responses.