IL17A and autoimmune disease: While Th1 cells have been considered pathogenic for MS/EAE, Th17 cells, a subpopulation of pro-inflammatory T helper cells defined by their secretion of IL-17 (4), have recently emerged as an important player in inflammatory and autoimmune diseases via the secretion of pro-inflammatory cytokines, such as IL-17A, IL-17F, GM-CSF, and IL-22 (5, 6).