Differential role of TNF-alpha and IFN-gamma in the brain of rats with chronic relapsing autoimmune encephalomyelitis

To elucidate the mechanisms of relapses of the clinical signs in experimental autoimmune encephalomyelitis (EAE), the cytokine profile of chronic relapsing EAE (CR-EAE) in rats was determined by competitive polymerase chain reaction (PCR). By immunization with guinea pig spinal cord homogenate and treatment with low-dose cyclosporin A (CsA), rats developed two attacks of EAE with remission in between. Cytokine analysis revealed that the level of TNF-alpha mRNA increased at the first and second attacks with transient disappearance at the remission phase. In contrast, the level of IFN-gamma mRNA was suppressed at the first attack by CsA and peaked at the second attack. Intraventricular administration of IFN-gamma prior to onset of disease signs induced more relapses, or a severe lethal form. In addition, the intraventricular injection of TNF-alpha caused the persistence of the clinical signs. These findings suggest that TNF-alpha contributes to the first and second attacks of CR-EAE, while IFN-gamma is not required for the first attack but is closely related to the relapse of the disease. With regard to anti-inflammatory cytokines, the levels of both TGF-beta1 and IL-10 mRNA at the second attack were higher than those at the first attack. Taken together, differential involvement of TNF-alpha and IFN-gamma is closely associated with the clinical features of CR-EAE.