CD4 costimulation is not required in a novel LPS-enhanced model of myasthenia gravis

Exploring the Gut Microbiome in Myasthenia Gravis

The human gut microbiota is vital for maintaining human health in terms of immune system homeostasis. Perturbations in the composition and function of microbiota have been associated with several autoimmune disorders, including myasthenia gravis (MG), a neuromuscular condition associated with varying weakness and rapid fatigue of the skeletal muscles triggered by the host’s antibodies against the acetylcholine receptor (AChR) in the postsynaptic muscle membrane at the neuromuscular junction (NMJ). It is hypothesized that perturbation of the gut microbiota is associated with the pathogenesis of MG. The gut microbiota community profiles are usually generated using 16S rRNA gene sequencing. Compared to healthy individuals, MG participants had an altered gut microbiota’s relative abundance of bacterial taxa, particularly with a drop in Clostridium. The microbial diversity related to MG severity and the overall fecal short-chain fatty acids (SCFAs) were lower in MG subjects. Changes were also found in terms of serum biomarkers and fecal metabolites. A link was found between the bacterial Operational Taxonomic Unit (OTU), some metabolite biomarkers, and MG’s clinical symptoms. There were also variations in microbial and metabolic markers, which, in combination, could be used as an MG diagnostic tool, and interventions via fecal microbiota transplant (FMT) could affect MG development. Probiotics may influence MG by restoring the gut microbiome imbalance, aiding the prevention of MG, and lowering the risk of gut inflammation by normalizing serum biomarkers. Hence, this review will discuss how alterations of gut microbiome composition and function relate to MG and the benefits of gut modulation.

Effects of Teriflunomide on B Cell Subsets in MuSK-Induced Experimental Autoimmune Myasthenia Gravis and Multiple Sclerosis

Antigen-specific immune responses are crucially involved in both multiple sclerosis (MS) and myasthenia gravis (MG). Teriflunomide is an immunomodulatory agent approved for treatment of MS through inhibition of lymphocyte proliferation. MG associated with muscle-specific tyrosine kinase (MuSK) antibodies often manifests with a severe disease course, prompting development of effective treatment methods. To evaluate whether teriflunomide treatment may ameliorate MuSK-autoimmunity, experimental autoimmune MG (EAMG) was induced by immunizing C57BL/6 (B6) mice three times with MuSK in complete Freund's adjuvant (CFA) (n = 17). MuSK-immunized mice were treated daily with teriflunomide (n = 8) or PBS (n = 9) starting from the third immunization (week 8) to termination (week 14). Clinical severity of EAMG was monitored. Immunological alterations were evaluated by measurement of anti-MuSK IgG, neuromuscular junction deposits, and flow cytometric analysis of lymph node cells. In MS patients under teriflunomide treatment, the peripheral blood B cell subset profile was analyzed. B6 mice treated with teriflunomide displayed relatively preserved body weight, lower EAMG prevalence, reduced average clinical grades, higher inverted screen scores, diminished anti-MuSK antibody and NMJ deposit levels. Amelioration of EAMG findings was associated with reduced memory B cell ratios in the lymph nodes. Similarly, MS patients under teriflunomide treatment showed reduced memory B cell, plasma cell, and plasmablast ratios. Teriflunomide treatment has effectively ameliorated MuSK-autoimmunity and thus may putatively be used in long-term management of MuSK-MG as an auxiliary treatment method. Teriflunomide appears to exert beneficial effects through inhibition of effector B cells.

Review on Toll-Like Receptor Activation in Myasthenia Gravis: Application to the Development of New Experimental Models

Abnormal toll-like receptor (TLR) activation and uncontrolled resolution of inflammation are suspected to play a key role in the development of autoimmune diseases. Acquired myasthenia gravis (MG) is an invalidating neuromuscular disease leading to muscle weaknesses. MG is mainly mediated by anti-acetylcholine receptor (AChR) autoantibodies, and thymic hyperplasia characterized by ectopic germinal centers is a common feature in MG. An abnormal expression of certain TLRs is observed in the thymus of MG patients associated with the overexpression of interferon (IFN)-β, the orchestrator of thymic changes in MG. Experimental models have been developed for numerous autoimmune diseases. These models are induced by animal immunization with a purified antigen solubilized in complete Freund's adjuvant (CFA) containing heat-inactivated mycobacterium tuberculosis (MTB). Sensitization against the antigen is mainly due to the activation of TLR signaling pathways by the pathogen motifs displayed by MTB, and attempts have been made to substitute the use of CFA by TLR agonists. AChR emulsified in CFA is used to induce the classical experimental autoimmune MG model (EAMG). However, the TLR4 activator lipopolysaccharide (LPS) has proved to be efficient to replace MTB and induce a sensitization against purified AChR. Poly(I:C), the well-known TLR3 agonist, is also able by itself to induce MG symptoms in mice associated with early thymic changes as observed in human MG. In this review, we discuss the abnormal expression of TLRs in MG patients and we describe the use of TLR agonists to induce EAMG in comparison with other autoimmune experimental models.