Campylobacter jejuni induces transcellular translocation of commensal bacteria via lipid rafts

BACKGROUND Campylobacter enteritis represents a risk factor for the development of inflammatory bowel disease (IBD) via unknown mechanisms. As IBD patients exhibit inflammatory responses to their commensal intestinal microflora, factors that induce translocation of commensal bacteria across the intestinal epithelium may contribute to IBD pathogenesis. This study sought to determine whether Campylobacter induces translocation of non-invasive intestinal bacteria, and characterize underlying mechanisms. METHODS Mice were infected with C. jejuni and translocation of intestinal bacteria was assessed by quantitative bacterial culture of mesenteric lymph nodes (MLNs), liver, and spleen. To examine mechanisms of Campylobacter-induced bacterial translocation, transwell-grown T84 monolayers were inoculated with non-invasive Escherichia coli HB101 +/- wild-type Campylobacter or invasion-defective mutants, and bacterial internalization and translocation were measured. Epithelial permeability was assessed by measuring flux of a 3 kDa dextran probe. The role of lipid rafts was assessed by cholesterol depletion and caveolin co-localization. RESULTS C. jejuni 81-176 induced translocation of commensal intestinal bacteria to the MLNs, liver, and spleen of infected mice. In T84 monolayers, Campylobacter-induced internalization and translocation of E. coli occurred via a transcellular pathway, without increasing epithelial permeability, and was blocked by depletion of epithelial plasma membrane cholesterol. Invasion-defective mutants and Campylobacter-conditioned cell culture medium also induced E. coli translocation, indicating that C. jejuni does not directly 'shuttle' bacteria into enterocytes. In C. jejuni-treated monolayers, translocating E. coli associated with lipid rafts, and this phenomenon was blocked by cholesterol depletion. CONCLUSION Campylobacter, regardless of its own invasiveness, promotes the translocation of non-invasive bacteria across the intestinal epithelium via a lipid raft-mediated transcellular process.