A previous work on Plantago palmata polysaccharides (PS) attributed immunomodulatory properties of leaves to a polysaccharide fraction (PS50) that stimulated NO and TNF-α production by interferon gamma- (IFN-γ-) activated macrophages. The present work aims to elucidate the chemical structure of these immunomodulatory polysaccharides. Size exclusion chromatography showed that the active polymers present an active fraction with a very high molecular weight (about 1200？kDa). These polysaccharides are pectic in nature, with a predominantly unbranched galacturonan domain and with a domain bearing side chains that consist of highly branched arabinan, galactan, and/or arabinogalactan. Comparatively to the well-known Plantago major biologically active PS, Plantago palmata PS50 contained less arabinogalactan-proteins (AGPs) and had a different composition in glucose, galactose, and galacturonic acid. DNA contamination of the polysaccharide was estimated at about 0.04%, a concentration much lower than those reported immunomodulatory in hyaluronic acid preparations (3 to 15%). Therefore, the eventuality of a contaminating DNA-mediated biological activity could be ruled out. 1. Introduction Plantago palmata grows in the humid mountain regions of intertropical Africa at 1800 to 3000？m [1] and is widely used in traditional medicine in Burundi, Rwanda and South Kivu (Democratic Republic of Congo). Its leaves are often used as herbal remedies in the treatment of a number of diseases such as wounds, hepatitis, parasitic or infectious diseases, and pregnancy, and lactation troubles. They are also used for the improvement of health after disease [2, 3]. A survey of the literature indicates a certain convergence between these medicinal uses (antibacterial, antifungal, antiviral and, immunomodulatory) and those of other Plantago species [4–11]. This led us to investigate three groups of Plantago metabolites possibly related to these traditional uses and biological activities, that is, iridoids, phenylethanoid glycosides and polysaccharides [3, 12]. We previously showed that Plantago palmata leaves (i) contain appreciable amounts of iridoids and phenylethanoid glycosides, with aucubin and acteoside as major compounds [2]; (ii) present immunomodulatory properties, which could be attributed to polysaccharides (PS) [3].The effects of crude extracts and fractions obtained by high performance liquid chromatography/size exclusion chromatography (SEC) were investigated by the measurement of nitric oxide (NO), tumor necrosis factor-alpha (TNF-α), and interleukin-10 (IL-10)
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