Changes in the composition of rat peritoneal cells and their response to stimulation by selected gut microbiota during colitis

Abstract

BACKGROUND Deregulation of the immune response to microbiota or pathogens, and increased intestinal permeability have been proposed as disease-driving mechanisms in colitis. Since peritoneal macrophages guard the sterility of peritoneal cavity from bacterial leakage from the gut, it is plausible to assume that peritoneal macrophages are involved in colitis development. OBJECTIVES The objective was to investigate changes in the composition of peritoneal cells and their response to stimulation by selected gut microbiota during colitis. METHODS Seven days following induction of colitis with intrarectal instillation of ethanol or trinitrobenzenesulfonic acid (TNBS, 10mg/kg or 40mg/kg), peritoneal cells of Dark Agouti (DA) rats were isolated and subjected to flow cytometry. The amount of IL-6 and TNF-α produced by adherent cells was determined by ELISA following in vitro stimulation with LPS and commensal E.coli and Enteroccocus spp. RESULTS Instillation of ethanol or TNBS (10 and 40 mg/kg) increased the proportion of CD11bintCD4low monocytes and decreased the proportion of resident CD163+MHCIIIo macrophages and CD163-MHCIIhi macrophage/dendritic cells. In vitro treatment with Enterococcus spp. was superior over LPS and E.coli in increasing macrophage TNF-α release in all but saline-injected control rats. In vitro treatment with E.coli exceeded the level of LPS stimulation in inducing macrophage IL-6 release in saline- and ethanol-injected rats. It may be concluded that changes in the composition of peritoneal cells during colitis and, subsequently, their selectively altered response to gut commensals may perpetuate or modulate inflammation during disease development