Campylobacter jejuni induces transcytosis of commensal bacteria across the intestinal epithelium through M-like cells

Abstract

Background: Recent epidemiological analyses have implicated acute Campylobacter enteritis as a factor that may incite or exacerbate inflammatory bowel disease (IBD) in susceptible individuals. We have demonstrated previously that C. jejuni disrupts the intestinal barrier function by rapidly inducing epithelial translocation of non-invasive commensal bacteria via a transcellular lipid raft-mediated mechanism ('transcytosis'). To further characterize this mechanism, the aim of this current study was to elucidate whether C. jejuni utilizes M cells to facilitate transcytosis of commensal intestinal bacteria.

Results: C. jejuni induced translocation of non-invasive E. coli across confluent Caco-2 epithelial monolayers in the absence of disrupted transepithelial electrical resistance or increased permeability to a 3 kDa dextran probe. C. jejuni-infected monolayers displayed increased numbers of cells expressing the M cell-specific marker, galectin-9, reduced numbers of enterocytes that stained with the absorptive enterocyte marker, Ulex europaeus agglutinin-1, and reduced activities of enzymes typically associated with absorptive enterocytes (namely alkaline phosphatase, lactase, and sucrase). Furthermore, in Campylobacter-infected monolayers, E. coli were observed to be internalized specifically within epithelial cells displaying M-like cell characteristics.

Conclusion: These data indicate that C. jejuni may utilize M cells to promote transcytosis of non-invasive bacteria across the intact intestinal epithelial barrier. This mechanism may contribute to the inflammatory immune responses against commensal intestinal bacteria commonly observed in IBD patients.

Figure 1

Representative epifluorescent micrographs of Caco-2 monolayers stained with the absorptive enterocyte marker Ulex europaeus agglutinin-1 (red), the M-like cell specific marker galectin-9 (green diffuse cellular staining), and Hoechst nuclear stain (blue). (a) Monolayers treated with GFP Escherichia coli C25 (arrows) and C. jejuni 81-176. (b) Monolayers treated with only GFP E. coli C25 (control). Bar = 2 μm.

Figure 2

Confocal laser sections of Caco-2 monolayers treated with C. jejuni 81-176 plus non-invasive GFP Escherichia coli C25 (arrows) and stained with the absorptive enterocyte marker Ulex europaeus agglutinin-1 (red). E. coli are color-coded according to their respective depth within the monolayer from extracellular (yellow) to intracellular (blue). (a) Merge of all confocal laser sections. (b-e) Representative confocal laser sections starting from the apical surface of the monolayer (E. coli color-coded yellow) to the basolateral surface of the monolayer (E. coli color-coded blue).