IL17A and fibrosis: IL-21 can also promote tissue fibrosis through the induction of differentiation into Th17 cells [254,255], which produce a well-known profibrotic interleukin, IL-17, and which is involved in the development of fibrosis in various organs [256,257,258], although a recent study has suggested IL-17 plays an antifibrotic role in tubulointerstitial fibrosis [259].