Implication of double-stranded RNA signaling in the etiology of autoimmune myasthenia gravis

Objective Myasthenia gravis (MG) is an autoimmune disease mediated mainly by antiacetylcholine receptor (AChR) antibodies. The thymus plays a primary role in MG pathogenesis. As we recently showed an inflammatory and antiviral signature in MG thymuses, we investigated whether pathogen-sensing molecules could contribute to an anti-AChR response. Methods We studied the effects of toll-like receptor agonists on the expression of -AChR and various tissue-specific antigens (TSAs) in human thymic epithelial cell (TEC) cultures. As polyinosinicpolycytidylic acid (poly[I:C]), which mimics double-stranded RNA (dsRNA), stimulated specifically -AChR expression, the signaling pathways involved were investigated. In parallel, we analyzed the expression of dsRNA-signaling components in the thymus of MG patients, and the relevance of our data was investigated in vivo in poly(I:C)-injected mice. Results We demonstrate that dsRNA signaling induced by poly(I:C) specifically triggers the overexpression of -AChR in TECs and not of other TSAs. A poly(I:C) effect was also observed on MG TECs. This induction is mediated through toll-like receptor 3 (TLR3) and protein kinase R (PKR), and by the release of interferon (IFN)-. In parallel, human MG thymuses also display an overexpression of TLR3, PKR, and IFN-. In addition, poly(I:C) injections specifically increase thymic expression of -AChR in wild-type mice, but not in IFN-I receptor knockout mice. These injections also lead to an anti-AChR autoimmune response characterized by a significant production of serum anti-AChR antibodies and a specific proliferation of B cells. Interpretation Because anti-AChR antibodies are highly specific for MG and are pathogenic, dsRNA-signaling activation could contribute to the etiology of MG. ANN NEUROL 2013;73:281293