Preclinical models illustrate mechanisms of how IL-17 may contribute to skin [35,48,57,58], liver [59,60] and lung [61] GVHD, but the role of IL-17 is debated in some organs like the gut, where Th17 cells also play an important role in homeostasis [47,62]. The gene discussed is IL17A; the disease is graft versus host disease.