In Mali and other West African countries, the leaves of the tree Syzygium guineenseare utilized in the traditional medicine against various ailments such as wound healing, ulcers, diarrhoea, rheumatism and infections. The immune modulating activity may in part be conferred by pectic polysaccharides, which is a major constituent of the plant cell wall. Previous studies on pectic polysaccharides from the leaves of Malian medicinal trees have shown that they posses several immunological activities. In the present study, we have isolated and characterised two immunologically active polysaccharide fractions from the leaves of S. guineense. One of the fractions contained an arabinogalactan type II polysaccharide, called Sg50A1, while the other polysaccharide fraction was a mixture of oligosaccharides of the pectic type, called Sg50A2. Both polysaccharides had high complement fixing ability, as well as the ability to stimulate nitric oxide release from macrophages, up-regulation of CD86 on dendritic cells, and proliferation of B cells. Sg50A1 and Sg50A2 also stimulated the secretion of pro-inflammatory and anti-inflammatory cytokines from both B cells and dendritic cells. Collectively, these results indicate that the presence of arabinogalactan structures within the polysaccharides is important for immunological activity and that plant-derived polysaccharides may be able to influence inflammatory processes.
Key words: Pectic polysaccharides, arabinogalactan, Syzygium guineense, immunomodulation.
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