MECHANISMS OF SALMONELLA CLEARANCE BY NEUTROPHILS IN THE INTESTINAL LUMEN

Abstract Salmonella infection is one of the leading causes of enteric diseases in humans, with symptoms resemblinginflammatory bowel diseases (IBD), which include bloody diarrhea, abdominal cramps and fever. IngestedSalmonella rapidly colonizes the gut lumen prior to invasion of the mucosal tissue, causing barrier dysfunctionand rapid recruitment of neutrophils (PMNs) to the intestinal mucosa and the luminal space. While, PMNaccumulation in the intestinal lumen is a prominent histological feature of gut inflammation, the fate andfunction of PMNs in the luminal space is not known. Similarly, whether PMNs that infiltrate the intestinal lumenare capable of Salmonella uptake, and whether they can efficiently navigate to pathogen colonization foci is notclear.This highlights the need to better understand the regulation of PMN trafficking in inflamed intestine andmechanistic 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 Salmonellainfection. Using this approach, we confirmed that Salmonella infection triggers PMN accumulation at theluminal 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 luminallocomotion 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 testthe 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 helpidentify new molecular targets to limit infection-mediated inflammation and injury.