Experiments in the experimental autoimmune encephalomyelitis MS mouse model have shown that Th17 cells induce ectopic lymphoid structures in the subarachnoid space, where they acquire a Tfh phenotype (27) and also that Th cells producing both IFNγ and IL-17 were more pathogenic than Th cells producing IFNγ or IL-17 alone (5). The gene discussed is IL17A; the disease is experimental autoimmune encephalomyelitis.