TREM1 signaling amplifies neutrophil-mediated inflammation in inflammatory bowel disease

In inflammatory bowel disease (IBD), complex immune dysregulation induces chronic inflammation. TREM1 is a receptor expressed on myeloid cells and is activated by ligands such as PGLYRP1 to amplify inflammatory responses. Here, we analyze the function of TREM1 signaling in neutrophil-driven inflammation, identifying two positive feedback loops. First, neutrophils activated by phorbol 12-myristate 13-acetate (PMA) or by bacteria release PGLYRP1, which forms a ligand complex with bacterial peptidoglycan and activates TREM1, thereby enhancing neutrophil degranulation, reactive oxygen species production, and NETosis. Second, TREM1 activation on monocytes promotes the secretion of chemokines and cytokines that recruit and activate additional neutrophils, further perpetuating inflammation. In vivo, TREM1 activation exacerbates colitis in mice, with the gut commensal bacterium Blautia faecis potentially contributing to human TREM1 activation in IBD. In biopsy samples from patients with IBD, an elevated TREM1 pathway signature is associated with inflamed tissue and treatment resistance in ulcerative colitis. Our findings thus highlight TREM1 as a regulator of mucosal inflammation, and a potential therapeutic target for IBD. TREM1 boosts inflammatory responses and has been implicated to promote pathogenic inflammation in inflammatory bowel disease (IBD). Here, the authors find self-amplifying positive feedback loops of neutrophil-specific TREM1 signaling exacerbating colitis, indicating TREM1 as potential target for IBD therapy.