Elevated concentrations of calprotectin in stool and plasma are detected in patients with active IBD and correlate well with disease activity.37 In addition, abnormally high levels of ROS in inflamed mucosa and concomitant imbalance between oxidants and antioxidants cause oxidative DNA damage to intestinal epithelial cells in IBD.38 Interestingly, we found that butyrate-treated neutrophils produced low levels of S100A8, S100A9, ROS, and MPO. Here, S100A9 is linked to inflammatory bowel disease.