Enteroaggregative Escherichia coli expresses a novel flagellin that causesIL-8 release from intestinal epithelial cells

Enteroaggregative Escherichia coli (EAEC) is an emerging cause of acute and persistent diarrhea worldwide. EAEC infections are associated with intesti nal inflammation and growth impairment in infected children, even in the ab sence of diarrhea. We previously reported that prototype EAEC strains rapid ly induce IL-8 production by Caco-2 intestinal epithelial cells, and that t his effect is mediated by a soluble, heat-stable factor released by these b acteria in culture. We herein report the cloning, sequencing, and expressio n of this biologically active IL-8-releasing factor from EAEC, and its iden tification as a flagellin that is unique among known expressed proteins. Fl agella purified from EAEC 042 and several other EAEC isolates potently rele ase IL-8 from Caco-2 cells; an engineered aflagellar mutant of 042 does not release IL-8. Finally, cloned EAEC flagellin expressed in nonpathogenic E. coli as a polyhistidine-tagged fusion protein maintains its proinflammator y activity These findings demonstrate a major new means by which EAEC may c ause intestinal inflammation, persistent diarrhea, and growth impairment th at characterize human infection with these organisms. Furthermore, they ope n new approaches for diagnosis and vaccine development. This novel pathogen ic mechanism of EAEC extends an emerging paradigm of bacterial flagella as inflammatory stimuli.