MS patients’ cerebral fluid contains immune cells that generate IL-17 mRNA.228 Moreover, in patients with MS, Th17 cells penetrate the blood-brain barrier and assemble in regions with active lesions.229 In a proof-of-concept study, administering anti-IL-17 (secukinumab) therapy to patients with relapsing-remitting MS led to a 67% decrease in the number of new lesions.230 Unfortunately, despite promising results in patients with MS and compelling evidence from the EAE animal model, this has not been pursued in extensive clinical trials. Here, IL17A is linked to relapsing-remitting multiple sclerosis.