IL21 and inflammatory bowel disease: Th17 ​cells, induced by TGF-β and IL-6 and identified by the secretion of amounts of IL-17A, IL-17F, IL-21 and IL-22 [55], can promote inflammatory cytokines and chemokines (such as MCP-1 and MIP-2), cyclooxygenase-2, tissue degradation proteases (MMPs) and matrix metalloproteinases, etc., causing inflammatory cell infiltration and tissue destruction [56,57], thus aggravating IBD.