Myeloperoxidase (MPO) is a specific polymorphonuclear enzyme that is most abundantly expressed in neutrophil granulocytes. It functions in the oxygen-dependent killing of microorganisms and is released from primary granules of neutrophils during acute inflammation. MPO is encoded by the MPO gene, which is about 11kb and composed of 11 introns and 12 exons, located in chromosome 17 (q12-24). The mature 150 kDa MPO protein is a dimer consisting of two 15kDA light chains and two heavy chains in variable degrees of glycosylation.
MPO activity has been found to be linearly related to neutrophil cell count. Since neutrophils play a predominant role in inflammatory and immune reactions in inflammatory bowel disease (IBD) and MPO has been observed both in the intestinal mucosa and gut lavage, the determination of MPO in stool sample provides one of the most sensitive and promising biomarkers in predicting disease severity.