IL17A and inflammatory bowel disease: Inhibiting pro-inflammatory cytokines and maintaining anti-inflammatory cytokines. Pro-inflammatory cytokines (tumor necrosis factor-alpha (TNF-α), IL-1, IL-6, IL-12, IL-17, IL-18, IL-21 and IL-23), especially IL-6, TNF-α and IL-1β, are associated with the initiation and progression of IBD [7,40,83], which result from recruited monocytes and activated macrophages.