Abstract

Recombinant interferon beta (IFNbeta) benefits patients with relapsing remitting multiple sclerosis (MS), but the mechanisms of action are unknown. We studied in vivo immunologic effects of IFNbeta treatment and their relationship to clinical efficacy. Cytokines were measured in blood and CSF from MS patients participating in a placebo-controlled phase III clinical trial and an open-label phase IV [corrected] tolerability study of IFNbeta-1a. Additionally, immunologic studies were conducted in animals with proteolipid protein (PLP)-induced chronic relapsing experimental autoimmune encephalomyelitis. Single intramuscular (IM) injections of IFNbeta-1a (6 MIU, 30 microg) were associated with significant in vivo upregulation of interleukin-10 (IL-10) and IL-4 but not IFNgamma mRNA in peripheral blood mononuclear cells. Forty-eight hours after each IFNbeta-1a injection, serum IL-10 levels increased and remained elevated for 1 week. IFNbeta-1a recipients in the placebo-controlled phase III clinical trial showed significantly increased concentrations of CSF IL-10 after 2 years of treatment. This response correlated with a favorable therapeutic response. Exposure of PLP-reactive murine T-cell lines to IFNbeta resulted in increased antigen-driven expression of IL-4 and IL-10 and reduced encephalitogenicity. IFNbeta-1a injections induce systemic and intrathecal immunosuppressive cytokines. Myelin-specific T cells treated with IFNbeta-1a demonstrate increased immunosuppressive cytokine expression and reduced encephalitogenicity. The relationship between increased CSF IL-10 and response to therapy suggests that induction of IL-10 is a mechanism underlying IFNbeta-1a effects in MS patients.