Induction of inflammation by Escherichia coli on the mucosal level: requirement for adherence and endotoxin

Abstract

Bacterial infection of the mouse urinary tract is followed by the recruitment of leukocytes to the mucosal surface. This study examined the bacterial components involved in the induction of this response. Escherichia coli of serotype O75:K5:H- expressing adhesins specific for the Gal alpha 1-4Gal beta- (Gal, galactose) and mannose-containing receptors were instilled into the urinary bladder of lipopolysaccharide responder (C3H/HcN) and lipopolysaccharide nonresponder (C3H/HeJ) mice. The inflammation was quantitated as the number of leukocytes excreted into the urine at various times after infection. The response was first shown to depend on the Lps genotype of the mouse. The leukocyte excretion that occurred within 24 h after infection of C3H/HeN mice was absent in C3H/HeJ mice. The components triggering the response were present on both live and Formalin-killed bacterial cells, and the response was mimicked by intravesical inoculation of isolated lipid A. Pretreatment of bacteria with soluble receptor oligosaccharides resulted in inhibition of attachment in vitro and of the inflammation in vivo. A direct synergy between adhesins specific for Gal alpha 1-4Gal beta receptors and lipid A was demonstrated. Mixtures of these components induced a leukocyte response higher than the sum of the responses to each component alone. These results suggest that the inflammation induced by gram-negative bacteria in the urinary tract can be triggered at the level of the epithelial cells by endotoxin presented by an attaching bacterial cell and that intact function at the Lps locus of the host is required for this to occur.