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

F. Ammoscato1, P. Biancheri1, A. Di Sabatino2, R. Curciarello1, L. Kruidenier3, G.R. Corazza2, T.T. MacDonald1, 1Blizard Institute, Barts and The London School of Medicine and Dentistry, Centre for Immunology and Infectious Disease, London, United Kingdom, 2Fondazione IRCCS Policlinico S. Matteo, University of Pavia, First Department of Medicine, Pavia, Italy, 3GlaxoSmithKline, Immuno-Inflammation CEDD, Stevenage, United Kingdom

Background

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. TREM-1 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.

Conclusion

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.