Molecular mechanisms of high-dose antigen therapy in experimental autoimmune encephalomyelitis: Rapid induction of Th1-type cytokines and inducible nitric oxide synthase

High-dose hg administration induces apoptotic death of autoreactive T cells and is an effective therapy of experimental autoimmune diseases of the ner vous system. To explore the role of cytokines in Ag-specific immunotherapy, we analyzed mRNA induction and protein expression for the proinflammatory cytokines TNF-alpha and IFN-gamma, the anti-inflammatory cytokine IL-10, an d the cytokine-inducible NO synthase (iNOS) during high-dose Ag therapy of adoptive transfer experimental autoimmune encephalomyelitis (AT-EAE) in the Lewis rat. Using semiquantitative and competitive RT-PCR, we found 5- to 6 -fold induction of TNF-alpha mRNA and 3-fold induction of IFN-gamma mRNA in the spinal cord that occurred within 1 h after i.v. injection of Ag and wa s accompanied by a 2-fold increase of iNOS mRNA, Both IFN-gamma and iNOS mR NA remained elevated for at least 6 h, whereas TNF-alpha mRNA was already d own-regulated 6 h after Ag injection. A comparable time course was found fo r circulating serum levels of TNF-alpha and IFN-gamma. IL-10 mRNA levels di d not change significantly following Ag injection, Neutralization of TNF-al pha by anti-TNF-alpha antiserum in vivo led to a significant decrease in th e rate of T cell and oligodendrocyte apoptosis induced by high-dose Ag admi nistration, but did not change the beneficial clinical effect of Ag therapy . Our data suggest profound activation of proinflammatory but not of anti-i nflammatory cytokine gene expression by high-dose Ag injection. Functionall y, TNF-alpha contributes to increased apoptosis of both autoaggressive T ce lls and oligodendrocytes in the target organ and may thereby play a dual ro le in this model of Ag-specific therapy of CNS autoimmune diseases.