Om intestinal epithelial cells, or inhibit eukaryotic protein synthesis resulting in intestinal injury[2?]. Pathogenic E. coli that breach the intestinal mucosal barrier are phagocytosed by innate immune cells such as lamina propria macrophages and neutrophils. Some pathogenic E. coli strains have also acquired virulence genes that allow them to avoid destruction within phagocytes and thereby promote disease[6]. For example, uptake of EHEC into macrophages is associated with increased expression of Shiga toxin, and Shiga toxin enhances intra-macrophage survival through an unknown mechanism[6,7]. Likewise, expression of nitric oxide reductase in EHEC enhances their survival within macrophage phagolysosomes presumably by protecting them from reactive nitrogen species [8]. Similar to pathogenic strains of E. coli, resident intestinal (commensal) E. coli also encounter lamina propria macrophages in the intestine, especially during periods of epithelial damage and enhanced mucosal permeability in chronic inflammatory lesions associated with the inflammatory bowel diseases (IBD’s), Crohn’s disease and ulcerative colitis. IBD’s are associated with genetically-determined defective innate immune responses including disordered cytokine secretion and bacterial clearance in macrophages[9,10]. In ZM241385 price addition IBD’s and experimental murine MK-5172 manufacturer colitis are associated with increased numbers of luminal commensal E. coli [11]. Therefore, it is plausible that enhanced survival of E. coli in macrophages may play a role in etiopathogenesis of IBD’s. Indeed, others have shown that resident adherent- invasive E. coli are more prevalent in inflamed ileal tissue from Crohn’s disease patients compared with controls and that a specific adherent-invasive E. coli strain isolated from a human Crohn’s disease patient causes experimental colitis in susceptible hosts in vivo and survives better in macrophages in vitro compared with laboratory reference E. coli strains[12?4]. The increased survival of the adherent-invasive E. coli strain in macrophages is due in part to expression of E. coli htrA, a gene that allows E. coli to grow at elevated temperatures and defend against killing by hydrogen peroxide in vitro[15]. Genes, including htrA, may therefore function as virulence factors in commensal E. coli by protecting the bacteria from toxic reactive oxygen species (ROS) and/or reactive nitrogen species (RNS) found in macrophage phagolysosomes. Similar to HtrA, the E. coli small heat shock proteins IbpA and IbpB also protect bacteria from killing by heat and oxidative stress in laboratory cultures[16?8]. The role of the ibpAB operon in protecting E. coli from heat damage is reinforced by evidence that ibpAB are upregulated in E. coli cultures in response to heat treatment[19,20]. In addition, we have previously shown that a commensal adherent-invasive murine strain of E. coli (NC101), which causes colitis in mono-colonized Il10-/- mice, increases ibpAB expression when present in the inflamed vs. healthy colon, possibly due to the increased concentrations of ROS/RNS in inflamed colon tissue[21?3]. However, it is unknown whether ibpAB are upregulated in response to ROS/RNS are important for the survival of non-pathogenic E. coli in macrophage phagolysosomes. We hypothesized that commensal E. coli upregulate ibpAB in response to ROS and that ibpAB protect E. coli from ROS-mediated killing within macrophages.PLOS ONE | DOI:10.1371/journal.pone.0120249 March 23,2 /IbpAB Protect Comme.Om intestinal epithelial cells, or inhibit eukaryotic protein synthesis resulting in intestinal injury[2?]. Pathogenic E. coli that breach the intestinal mucosal barrier are phagocytosed by innate immune cells such as lamina propria macrophages and neutrophils. Some pathogenic E. coli strains have also acquired virulence genes that allow them to avoid destruction within phagocytes and thereby promote disease[6]. For example, uptake of EHEC into macrophages is associated with increased expression of Shiga toxin, and Shiga toxin enhances intra-macrophage survival through an unknown mechanism[6,7]. Likewise, expression of nitric oxide reductase in EHEC enhances their survival within macrophage phagolysosomes presumably by protecting them from reactive nitrogen species [8]. Similar to pathogenic strains of E. coli, resident intestinal (commensal) E. coli also encounter lamina propria macrophages in the intestine, especially during periods of epithelial damage and enhanced mucosal permeability in chronic inflammatory lesions associated with the inflammatory bowel diseases (IBD’s), Crohn’s disease and ulcerative colitis. IBD’s are associated with genetically-determined defective innate immune responses including disordered cytokine secretion and bacterial clearance in macrophages[9,10]. In addition IBD’s and experimental murine colitis are associated with increased numbers of luminal commensal E. coli [11]. Therefore, it is plausible that enhanced survival of E. coli in macrophages may play a role in etiopathogenesis of IBD’s. Indeed, others have shown that resident adherent- invasive E. coli are more prevalent in inflamed ileal tissue from Crohn’s disease patients compared with controls and that a specific adherent-invasive E. coli strain isolated from a human Crohn’s disease patient causes experimental colitis in susceptible hosts in vivo and survives better in macrophages in vitro compared with laboratory reference E. coli strains[12?4]. The increased survival of the adherent-invasive E. coli strain in macrophages is due in part to expression of E. coli htrA, a gene that allows E. coli to grow at elevated temperatures and defend against killing by hydrogen peroxide in vitro[15]. Genes, including htrA, may therefore function as virulence factors in commensal E. coli by protecting the bacteria from toxic reactive oxygen species (ROS) and/or reactive nitrogen species (RNS) found in macrophage phagolysosomes. Similar to HtrA, the E. coli small heat shock proteins IbpA and IbpB also protect bacteria from killing by heat and oxidative stress in laboratory cultures[16?8]. The role of the ibpAB operon in protecting E. coli from heat damage is reinforced by evidence that ibpAB are upregulated in E. coli cultures in response to heat treatment[19,20]. In addition, we have previously shown that a commensal adherent-invasive murine strain of E. coli (NC101), which causes colitis in mono-colonized Il10-/- mice, increases ibpAB expression when present in the inflamed vs. healthy colon, possibly due to the increased concentrations of ROS/RNS in inflamed colon tissue[21?3]. However, it is unknown whether ibpAB are upregulated in response to ROS/RNS are important for the survival of non-pathogenic E. coli in macrophage phagolysosomes. We hypothesized that commensal E. coli upregulate ibpAB in response to ROS and that ibpAB protect E. coli from ROS-mediated killing within macrophages.PLOS ONE | DOI:10.1371/journal.pone.0120249 March 23,2 /IbpAB Protect Comme.
