MPO and colitis: The analysis of several parameters of inflammation, colon weight/colon length ratio (an indicator of overall colonic inflammation) and colonic myeloperoxidase (MPO) activity (a marker of tissue infiltration of neutrophils) as well as histological examination and scoring revealed a decrease of inflammation in mice transplanted with a WT microbiota (Fig. 3d, e and Supplementary Fig. 4d, e), indicating that colitis was more severe in mice receiving a WT microbiota than those receiving a PepT1−/− microbiota.