With regard to their function, iNKT cells from patients with MS were found to be defective in cytokine production [27,29], to be hyporesponsive to stimulation with α-GalCer in vitro [7,8] and to have a Th1/Th17 cytokine bias, which was most prominent in patients with secondary progressive MS, who displayed an increased production of IL-17 by either CD4+ CD8− or CD4−CD8+ iNKT cells [30]. This evidence concerns the gene IL17A and secondary progressive multiple sclerosis.