IL-9 is important for T-cell activation and differentiation in autoimmune inflammation of the central nervous system.

Immunization with the epitope induced EAE in mice. IL-9-/- mice were resistant to developing clinical EAE. IL-9-/- mice had lower incidence of disease (5/20) than wild type mice (20/20), and also a much milder clinical course and delayed onset. EAE-resistant IL-9(-/-) mice exhibited considerably fewer infiltrating immune cells in the CNS, with lower levels of IL-17 and IFN-gamma expression than their WT littermates. Treatment of mice with recombinant IL- 9 on day 0 to 30 post-immunization completely restored susceptibility to EAE in IL-9-/- mice. Disease was measured by histopathology.