Initial studies in the experimental autoimmune encephalitis model showed that IL-9 neutralization or IL-9 knock out could attenuate disease [14]–[15], [32] but recent studies indicate that IL-9 may also play a role in Treg function whereby the outcome of the autoimmune disease may depend on the IL-9 mediated regulation of the Treg/Th17 balance [34]. Here, IL9 is linked to autoimmune encephalitis.