It is now known that IL-17A has pro-inflammatory effects on a wide range of cellular targets, such as epithelium, endothelium, and monocytes/macrophages [8]–[10], and plays pathogenic roles in some organ-specific autoimmune diseases, such as rheumatoid arthritis (RA) and multiple sclerosis, as well as IBD [11]. Here, IL17A is linked to inflammatory bowel disease.