Oral administration of cholera toxin B subunit conjugated to myelin basic protein protects against experimental autoimmune encephalomyelitis by inducing transforming growth factor-beta-secreting cells and suppressing chemokine expression

The efficacy and mechanism of immunosuppression against experimental autoim mune encephalomyelitis (EAE) by oral low-dose administration of myelin basi c protein (MBP) conjugated to cholera toxin a subunit (CTB) were investigat ed in Lewis rats immunized with MBP together with complete Freund's adjuvan t 4 days before the start of treatment. Oral treatment with CTB-MBP conjuga te gave almost complete protection against disease, an effect that was tota lly abrogated by including a low dose of cholera holotoxin (CT). The protec tion by CTB-MBP was associated with a dramatic reduction in the number of l eukocytes staining for CD4, CD8, IL-2R or MHC class II in the spinal cord a s examined by immunohistochemistry. The mRNA expressions of T(h)1 cytokines IFN-gamma, IL-12 and tumor necrosis factor-alpha, as well as of chemokines monocyte chemotactic protein (MCP)-1 and RANTES in the spinal cord were al so reduced by 76-94%, as assessed by in situ hybridization. In contrast, tr ansforming growth factor (TGF)-beta mRNA-expressing cells were strongly inc reased in the spinal cord from animals treated orally with the CTB-MBP conj ugate. In the draining peripheral lymph nodes, the number of MBP-specific T GF-beta mRNA-expressing cells was also increased, whereas there was a decre ase in cells expressing T(h)1 or T(h)2 cytokine mRNA. Protection against EA E could be transferred by injection of cells from the mesenteric lymph node s of animals fed with CTB-MBP into naive animals exposed to encephalitogeni c T cells. The results indicate that the protective anti-inflammatory effec t by oral treatment with CTB-MBP conjugate is, to a large extent, due to th e induction of TGF-beta-secreting suppressive-regulatory T cells and to loc al down-regulation of MCP-1 and RANTES in the spinal cord.