P073 Ex vivo activation of triggering receptor expressed on myeloid cells 1 enhances the production of pro-inflammatory cytokines by inflammatory bowel disease mucosa

Abstract

BACKGROUND AND AIMS. Intestinal macrophages play a central role in the pathogenesis of inflammatory bowel disease (IBD). The phenotype of mucosal macrophages changes dramatically at the site of inflammation, where high numbers of CD33+CD68+ macrophages overexpress toll-like receptors, CD14 and triggering receptor expressed on myeloid cells 1 (TREM-1). TREM-1 is expressed on the surface of neutrophils and macrophages and contributes to the amplification of inflammatory responses by enhancing degranulation and secretion of pro-inflammatory mediators. After comparing the percentage of TREM-1-expressing macrophages in IBD versus control mucosa, we explored the ex vivo effects of an activating anti-TREM-1 antibody on the intestinal immune response in IBD. METHODS. Lamina propria mononuclear cells (LPMCs) were isolated from the inflamed colon of 11 IBD patients (5 ulcerative colitis and 6 Crohn's disease), and from normal colon of 8 control subjects, and the expression of CD68, CD33 and TREM-1 was analysed by flow cytometry. TREM1 mRNA expression in CD33+ LPMCs was evaluated by qRT-PCR. IBD biopsies from inflamed mucosa were cultured ex vivo with an activating anti-TREM-1 antibody or its control isotype, and the production of pro-inflammatory cytokines, namely interleukin (IL)1beta, IL-6 and IL-8, was determined by ELISA. RESULTS. The percentage of mucosal CD33+CD68+ macrophages was significantly (p,0.05) higher both in Crohn's disease and ulcerative colitis (17%±1.4 and 15%±7.6, respectively) in comparison to control subjects (6.0%±1.0). TREM-1 expression by mucosal macrophages was significantly (p,0.05) higher both in ulcerative colitis and in Crohn's disease (6.4%±0.2 and 4.4%±0.6) than in control subjects (0.8%±0.1). TREM-1 transcripts were significantly (p,0.05) higher in CD33+ LPMCs from inflamed IBD compared to control subjects. TREM-1 activation significantly (p,0.01) increased IL-1beta, IL-6 and IL-8 production by IBD biopsies cultured ex vivo. CONCLUSIONS. TREM-1 is overexpressed on macrophages infiltrating inflamed IBD mucosa, and its activation amplifies the production of pro-inflammatory cytokines. Further studies using chromatin immunoprecipitation assays are underway in order to establish whether TREM-1 overexpression in IBD may derive from epigenetic changes.