This polysaccharide A synthesized by Bacteroides fragilis prevents and treats colon inflammation in the rodents by stimulating an immunizing anti-inflammatory response dependent on the production of IL-10. Our digestive tract hosts more than 10¹⁴ micro-organisms divided into several hundreds of different bacteria. These bacteria are necessary to digestive homeostasis taking part in the development of the digestive tract, the production of vitamins, the digestion of fibres, the detoxification of pollutants, and the maturity of our immune system. Beyond the obvious therapeutic interest of this study using polysaccharide A of Bacteroides fragilis as treatment of the chronic inflammatory bowel diseases (IBD), this work suggests that the genome of mammals, limited to approximately 20.000 genes, does not code for all functions necessary to a good intestinal homeostasis and would be compensated by a symbiosis necessary with our microbiome representing several million genes.

(SK Mazmanian et al. Nature 2008 ; 453 : 620-5)