These include the gene S100A9, which forms the heterodimer calprotectin, and the antimicrobial peptide lipocalin (LCN2, also known as NGAL (Neutrophil Gelatinase-Associated Lipocalin)), both of which are used as fecal biomarkers for disease activity in inflammatory bowel disease [104,116,130,131,132]. Here, LCN2 is linked to inflammatory bowel disease.