P fimbriae-dependent, lipopolysaccharide-independent activation of epithelial cytokine responses

Cells in the mucosal barrier are equipped to sense and respond to microbes in the lumen and translate this molecular information into signals that can reach local or distant sites. The interaction of P-fimbriated Escherichia coil with human uroepithelial cells is a model to study the molecular mecha nism of epithelial cell activation by mucosal pathogens. Here, we examine t he role of lipopolysaccharide (LPS) as a co-stimulatory molecule in epithel ial cell activation by P-fimbriated E. coli. P-fimbriated clinical isolates or recombinant strains were shown to trigger a fimbriae-dependent epitheli al cell cytokine response. Mutational inactivation of the msbB sequences th at control lipid A myristoylation drastically impaired monocyte stimulation but not epithelial responses to P-fimbriated bacteria. Polymyxin B or bact ericidal/permeability increasing factor (BPI) neutralized the effects of li pid A in the monocyte assay, but did not reduce epithelial responses. Final ly, isolated LPS of the smooth, rough and deep rough chemotypes were poor e pithelial cell activators. The cells were shown to lack surface CD14 or CD1 4 mRNA as well as the CD14 co-receptor function and were also very poor LPS responders in the presence of human serum. These results demonstrate that epithelial cell responses to P-fimbriated E. coli are CD14 and LPS independ ent, and suggest that attaching pathogens can overcome the LPS unresponsive ness of epithelial cells by fimbriae-dependent activation mechanisms.