摘要AIM To investigate the specific pathogenesis of O-polysaccharide (O-PS) which is on the outer membrane of lipopolysaccharides (LPS) from Shigella flexneri.METHODS The O-PS was isolated and purified from Shigella flexneri 5 M90T by enzymatic hydrolysis and gel chromatography. Effects of O-PS were observed by in vitro experiment, (HeLa cell culture), and in vivo experiment (rabbit ileal loop assay).RESULTS In vitro and in vivo experiments with the purified O-PS from Shigella flexneri revealed that the O-PS alone was toxic to Hela cells and caused mucosal inflammation and hemorrhagic exudation in ileal loop of rabbit.DISCUSSION O-PS might be one of the factors causing diarrhea and its mechanism was different from endotoxin reaction of LPS. The molecular mechanism of O-PS need further studies.