Chemical composition and immunomodulatory activity of a pectic polysaccharide from the ground thistle Cirsium esculentum Siev.

► We determine the structure features and immunomodulatory activity of the pectic polysaccharide from the stems of the ground thistle Cirsium esculentum Siev. ► The backbone of cirsiuman consists of 1,4-D-galactopyranosyluronan blocks interconnected by 1,2-linked l-rhamnose residues. ► The side chains attach to the 4-position of the l-rhamnopyranose residues. ► We examine the immunomodulatory activity of cirsiuman at oral administration. Cirsiuman abrogates oral tolerance and evokes a predominant Th1 immune response to co-administered protein.