Roles of cytokines and T cells in the pathogenesis of myasthenia gravis

Abstract

Myasthenia gravis (MG) is characterized by muscle weakness and fatigue caused by the presence of autoantibodies against the acetylcholine receptor (AChR) or the muscle-specific tyrosine kinase (MuSK). Activated T, B and plasma cells, as well as cytokines, play important roles in the production of pathogenic autoantibodies and the induction of inflammation at the neuromuscular junction in MG. Many studies have focused on the role of cytokines and lymphocytes in anti-AChR antibody-positive MG. Chronic inflammation mediated by T helper type 17 (Th17) cells, the promotion of autoantibody production from B cells and plasma cells by follicular Th (Tfh) cells and the activation of the immune response by dysfunction of regulatory T (T_reg ) cells may contribute to the exacerbation of the MG pathogenesis. In fact, an increased number of Th17 cells and Tfh cells and dysfunction of T_reg cells have been reported in patients with anti-AChR antibody-positive MG; moreover, the number of these cells was correlated with clinical parameters in patients with MG. Regarding cytokines, interleukin (IL)-17; a Th17-related cytokine, IL-21 (a Tfh-related cytokine), the B-cell-activating factor (BAFF; a B cell-related cytokine) and a proliferation-inducing ligand (APRIL; a B cell-related cytokine) have been reported to be up-regulated and associated with clinical parameters of MG. This review focuses on the current understanding of the involvement of cytokines and lymphocytes in the immunological pathogenesis of MG, which may lead to the development of novel therapies for this disease in the near future.

Keywords: B cell; cytokine; lymphocyte; myasthenia gravis; treatment.

Fig. 1

Assumed networks of lymphocytes and cytokines in the pathogenesis of MG. Activated T cells, B cells, plasma cells and related cytokines play central roles in the production of pathogenic autoantibodies in myasthenia gravis (MG). Antigen‐presenting cells (APCs) present the acetylcholine receptor (AChR) or muscle‐specific tyrosine kinase (MuSK) to naive CD4⁺ T cells. Subsequently, T helper type 7 (Th17) cells, follicular Th (Tfh) cells and related cytokines are up‐regulated, whereas regulatory T (T_reg) cells and related cytokines are down‐regulated. Chronic inflammation by Th17 cells, the promotion of autoantibody production from B cells and plasma cells by Tfh cells or B cell‐related cytokines (B cell‐activating factor (BAFF) and a proliferation‐inducing ligand [APRIL]), and the activation of the immune response by dysfunction of T_reg cells may be involved in the pathogenesis of MG.