Systemic Macrophage Depletion Inhibits Helicobacter bilis-Induced Proinflammatory Cytokine-Mediated Typhlocolitis and Impairs Bacterial Colonization Dynamics in a BALB/cRag2−/−Mouse Model of Inflammatory Bowel Disease

Abstract

ABSTRACTHelicobacter bilis, an enterohepatic helicobacter, is associated with chronic hepatitis in aged immunocompetent inbred mice and inflammatory bowel disease (IBD) in immunodeficient mice. To evaluate the role of macrophages inH. bilis-induced IBD,Rag2−/−BALB/c or wild-type (WT) BALB/c mice were either sham dosed or infected withH. bilisMissouri strain under specific-pathogen-free conditions, followed by an intravenous injection of a 0.2-ml suspension of liposomes coated with either phosphate-buffered saline (control) or clodronate (a macrophage depleting drug) at 15 weeks postinfection (wpi). At 16 wpi, the ceca ofH. bilis-infectedRag2−/−mice treated with control liposomes had significantly higher histopathological lesional scores (for cumulative typhlitis index, inflammation, edema, epithelial defects, and hyperplasia) and higher counts of F4/80+macrophages and MPO+neutrophils compared toH. bilis-infectedRag2−/−mice treated with clodronate liposomes. In addition, cecal quantitative PCR analyses revealed a significant suppression in the expression of macrophage-related cytokine genes, namely,Tnfa,Il-1β,Il-10,Cxcl1, andiNos, in the clodronate-treatedH. bilis-infectedRag2−/−mice compared to theH. bilis-infectedRag2−/−control mice. Finally, cecal quantitative PCR analyses also revealed a significant reduction in bacterial colonization in the clodronate-treatedRag2−/−mice. Taken together, our results suggest that macrophages are critical inflammatory cellular mediators for promotingH. bilis-induced typhlocolitis in mice.