Myasthenia gravis (MG) and experimental autoimmune MG (EAMG) are antibody-mediated autoimmune diseases in which the nicotinic acetylcholine receptor (AChR) is the major autoantigen. Previously we have revealed that oral treatment with the less native recombinant fragment of the extracellular domain of the human AChR (Hα1-205) suppressed ongoing EAMG, whereas the more native recombinant Trx-Hα1-210 exacerbated EAMG. In this study, we speculated on the role of B-cell epitopes in oral tolerogens for the induction of oral tolerance in EAMG. We developed a B-cell epitope-free AChR fragment (BF-AChR) by removing two major B-cell epitopes (67-76 and 129-145) from Trx-Hα1-210. BF-AChR exhibited a poor response to EAMG sera and to AChR-specific B- and T-cells while its parent fragment, Trx-Hα1-210, showed much higher reactivity. Oral administration of BF-AChR ameliorated the symptoms in ongoing myasthenic rats accompanied by a significant decrease in AChR-specific humoral and Th1 cellular responses. The underlying mechanism for BF-AChR-induced oral tolerance was mediated by a shift from Th1 to regulatory T-cell (IL-10+, CD4+ TGF-β+ or Foxp3+) responses. This shift was assessed by changes in the cytokine profile and a deviation in the anti-AChR IgG isotypes from IgG2a/IgG2b to IgG1. Our results suggest that the removal of pathogenic B-cell epitopes from AChR fragments increases tolerogenicity by reducing the activation and proliferation of autoreactive B- and T-cells. Collectively, careful consideration of the immunogenicity of a tolerogen is necessary to induce successful oral tolerance in autoimmune disorders.
Bibliographical noteFunding Information:
We thank colleagues of the Immune Regulation and Tolerance laboratory in GIST for their help and encouragement. This work was supported by grants from the 21C Frontier Functional Human Genome Project, Korea Health 21 R&D Project, Ministry of Health & Welfare (A050533), the KBRDG initiative research program, the No. RTI05-01-01 from the regional technology innovation program of the MOCIE, the KRF funded by the Korean Government (KRF-2007-313-C00507) and systems biology infrastructure establishment grant provided by GIST in 2008.
- Autoimmune disease
- B-cell epitope
- Myasthenia gravis
- Oral tolerance