Mechanisms of Salmonella Clearance by Neutrophils in the Intestinal Lumen

Salmonella infection is one of the leading causes of enteric diseases in humans, with symptoms resembling inflammatory bowel diseases (IBD), which include bloody diarrhea, abdominal cramps and fever. Ingested Salmonella rapidly colonizes the gut lumen prior to invasion of the mucosal tissue, causing barrier dysfunction and rapid recruitment of neutrophils (PMNs) to the intestinal mucosa and the luminal space. While, PMN accumulation in the intestinal lumen is a prominent histological feature of gut inflammation, the fate and function of PMNs in the luminal space is not known. Similarly, whether PMNs that infiltrate the intestinal lumen are capable of Salmonella uptake, and whether they can efficiently navigate to pathogen colonization foci is not clear. This highlights the need to better understand the regulation of PMN trafficking in inflamed intestine and mechanistic aspects of PMN-mediated pathogen clearance. To this purpose, we have developed and optimized a novel imaging approach, allowing in real-time, visualization of the intestinal luminal surface, and the luminal behavior of infiltrating PMNs following Salmonella infection. Using this approach, we confirmed that Salmonella infection triggers PMN accumulation at the luminal epithelial surface. We further found that adherent PMNs exhibited CD11b-dependent motile behavior (locomotion) along the apical epithelial membrane. Ex vivo, PMN motility was critical for Salmonella uptake, suggesting that PMNs can clear invading pathogens in the intestinal lumen, and by means of luminal locomotion can efficiently navigate to sites of colonizing bacterium to prevent spreading. Thus, we propose the use of this novel imaging approach (that we have developed in our laboratory), to test the hypothesis that PMN locomotion is necessary for clearance of enteric pathogens in the gut lumen, and for preventing Salmonella-induced symptomatic disease. These studies will define new mechanisms of PMN trafficking and pathogen clearance in the gut, and help identify new molecular targets to limit infection-mediated inflammation and injury.