MPO and inflammatory bowel disease: Although the precise etiology and pathology of IBD remain unclear, multifactorial pathological injury (e.g. compromised epithelial barrier integrity) and dysregulated innate and adaptive immune responses are proved to be associated with the pathogenesis of IBD.23,24 Massive recruitment and accumulation of neutrophils are observed in the intestinal mucosa of IBD, accompanied with upregulated levels of protein arginine deiminase 4, elastase, MPO and NETs in the colonic mucosa of UC patients, even in clinical remission.4,25,26