Clinical symptoms in MOG-induced EAE mice significantly exacerbated following hondroitin sulfate A (CS-A) injection, whereas administration of a degraded product, CSPG-DS, caused dramatic inhibition of EAE development. Also, administration of CSPG-DS but not CS-A, after the onset of clinical symptoms of EAE, was able to suppress the disease. Further studies demonstrated that CS-A up-regulated STAT4 expression and thus, induced IFN-γ production and Th1 CD4 T cell differenttiation. CS-A also up-regulated STAT3 and IL-23 expression and thus increased IL-17 producing T cells. CSPG-DS treatment both in vivo and in vitro decreased TNFα production from splenocytes. In vitro and in vivo studies indicated that CSPG-DS treatment in EAE mice significantly blocked migration of lymphocytes, whereas CS-A treatment increased lymphocyte infiltration in the brain.