A Natural Variant of the Signaling Molecule Vav1 Enhances Susceptibility to Myasthenia Gravis and Influences the T Cell Receptor Repertoire.

Isabelle Bernard,Mehdi Benamar,Nicolas Fazilleau,Antoine Sacquin,Mylène Gador,Sahar Kassem,Corine Pérals,Céline Colacios,Abdelhadi Saoudi

doi:10.3389/fimmu.2018.02399

Abstract

The guanine nucleotide exchange factor Vav1 is essential for transducing T cell receptor (TCR) signals and plays an important role in T cell development and activation. Previous genetic studies identified a natural variant of Vav1 characterized by the substitution of an arginine (R) residue by a tryptophane (W) at position 63 (Vav1R63W). This variant impacts Vav1 adaptor functions and controls susceptibility to T cell-mediated neuroinflammation. To assess the implication of this Vav1 variant on the susceptibility to antibody-mediated diseases, we used the animal model of myasthenia gravis, experimental autoimmune myasthenia gravis (EAMG). To this end, we generated a knock-in (KI) mouse model bearing a R to W substitution in the Vav1 gene (Vav1R63W) and immunized it with either torpedo acetylcholine receptor (tAChR) or the α146-162 immunodominant peptide. We observed that the Vav1R63W conferred increased susceptibility to EAMG, revealed by a higher AChR loss together with an increased production of effector cytokines (IFN-γ, IL-17A, GM-CSF) by antigen-specific CD4+ T cells, as well as an increased frequency of antigen-specific CD4+ T cells. This correlated with the emergence of a dominant antigen-specific T cell clone in KI mice that was not present in wild-type mice, suggesting an impact on thymic selection and/or a different clonal selection threshold following antigen encounter. Our results highlight the key role of Vav1 in the pathophysiology of EAMG and this was associated with an impact on the TCR repertoire of AChR reactive T lymphocytes.

Highlights

Myasthenia gravis (MG), a disabling neuromuscular disease, is a T cell-dependent, B cellmediated autoimmune disease in which autoantibodies directed against antigens located at the neuromuscular junction (NMJ) cause defective neuromuscular transmission [1,2,3]
These data show that Vav1R63W favors the development of experimental autoimmune MG (EAMG) and this was not associated with the disruption of B cell response
At day 9, which corresponds to the peak of the effector response, we selectively focused on CD4+ cells by cells producing cytokines was determined by intracytoplasmic staining after 72 h stimulation with (1 μM) or without α146-162 Acetylcholine receptor (AChR) peptide. (B) Histograms represent the Mean Fluorescence Intensity (MFI) of IFN-γ, IL-17A and GM-CSF expression by T cell receptor (TCR)+CD4+ LN cells

Summary

Introduction

Myasthenia gravis (MG), a disabling neuromuscular disease, is a T cell-dependent, B cellmediated autoimmune disease in which autoantibodies directed against antigens located at the neuromuscular junction (NMJ) cause defective neuromuscular transmission [1,2,3]. A better understanding of the etiology of MG and the pathways leading to disease induction may provide rational bases for developing new treatments. In this regard, experimental autoimmune MG (EAMG) models have been instrumental over the years for a better understanding of the pathophysiological role of specific autoantibodies and T helper lymphocytes, because they closely mimic human MG in its clinical and immunopathological manifestations. In EAMG, it has been shown that anti-AChR antibodies bind to the AChR at the neuromuscular junction, activate complement and accelerate AChR destruction, thereby leading to neuromuscular transmission failure and fatigable muscle weakness

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Results

Conclusion