Protective molecular mimicry in experimental myasthenia gravis

Experimental Autoimmune Myasthenia Gravis (EAMG): from immunochemical characterization to therapeutic approaches

Myasthenia Gravis (MG) is an organ-specific autoimmune disease. In high percentage of patients there are autoantibodies to the nicotinic acetylcholine receptor (AChR) that attack AChR on muscle cells at the neuromuscular junction, resulting in muscle weakness. Experimental Autoimmune Myasthenia Gravis (EAMG) is an experimental model disease for MG. EAMG is induced in several animal species by immunization with acetylcholine receptor (AChR), usually isolated from the electric organ of electric fish, which is a rich source for this antigen. Our lab has been involved for several decades in research of AChR and of EAMG. The availability of an experimental autoimmune disease that mimics in many aspects the human disease, provides an excellent model system for elucidating the immunological nature and origin of MG, for studying various existing treatment modalities and for attempting the development of novel treatment approaches. In this review in honor of Michael Sela and Ruth Arnon, we report first on our early pioneering contributions to research on EAMG. These include the induction of EAMG in several animal species, early attempts for antigen-specific treatment for EAMG, elicitation and characterization of monoclonal antibodies and anti-idiotypic antibodies, measuring humoral and cellular AChR-specific immune responses in MG patient and more. In the second part of the review we discuss more recent studies from our lab towards developing and testing novel treatment approaches for myasthenia. These include antigen-dependent treatments aimed at specifically abrogating the humoral and cellular anti-AChR responses, as well as immunomodulatory approaches that could be used either alone, or in conjunction with antigen-specific treatments, or alternatively, serve as steroid-sparing agents.

Myasthenia gravis: predictive factors associated with the synchronized elevation of anti-acetylcholine receptor antibody titer in Kanazawa, Japan

For a brief period, an increased incidence of elevated anti-acetylcholine receptor antibody titer was observed in patients with myasthenia gravis (MG) in Kanazawa, Japan. The purpose of this study was to examine the predictive factors associated with this antibody titer elevation. Decreased odds of titer elevation were seen in patients with early-onset MG than in those with late-onset MG. In patients with non-thymoma-related MG, thymectomy prevented the antibody titer elevation. Our data suggest that late-onset MG may have a different immunogenic response and the thymus might play an immunoregulatory role against extrinsic factors in some types of MG.

Role of immunologic cross-reactivity in neurological diseases

Although the immune system evolved to protect the host from foreign infection, it can sometimes recognize and attack host tissues, a phenomenon known as autoimmunity. In addition to genetic factors, environmental elements such as viruses and bacteria are thought to play a role in the development of autoimmune diseases. The major hypothesized mechanism by which infection with these agents can lead to autoimmunity is termed molecular mimicry. Here, immune responses initiated against foreign antigens are cross-reactive with self-antigens. This is thought to occur especially if the foreign antigen is similar in structure or amino acid sequence to the self-antigen. In this review, we explore evidence for the role of molecular mimicry in neurological diseases.

A comparison of epitope repertoires associated with myasthenia gravis in humans and nonhuman hosts

Here we analyzed the molecular targets associated with myasthenia gravis (MG) immune responses, enabled by an immune epitope database (IEDB) inventory of approximately 600 MG-related epitopes derived from 175 references. The vast majority of epitopes were derived from the α-subunit of human AChR suggesting that other MG-associated autoantigens should be investigated further. Human α-AChR was mostly characterized in humans, whereas reactivity primarily to T. californica AChR was examined in animal models. While the fine specificity of T-cell response was similar in the two systems, substantial antibody reactivity to the C-terminus was detected in the nonhuman system, but not in humans. Further analysis showed that the reactivity of nonhuman hosts to the C-terminus was eliminated when data were restricted to hosts tested in the context of autoimmune disease (spontaneous or induced), demonstrating that the epitopes recognized in humans and animals were shared when disease was present. Finally, we provided data subsets relevant to particular applications, including those associated with HLA typing or restriction, sets of epitopes recognized by monoclonal antibodies, and epitopes associated with modulation of immunity or disease. In conclusion, this analysis highlights gaps, differences, and similarities in the epitope repertoires of humans and animal models.

Molecular mimicry and auto-immunity

The term "molecular mimicry" was coined by R. Damian in 1964, who was first to suggest that antigenic determinants of micro-organisms may resemble antigenic determinants of their host. Damian suggested that this similarity served as a defense mechanism of a microorganism from the host's immune system and prevented the development of immune response to the micro-organism, thereby protecting it from host defense. Years later, the term "molecular mimicry" was attributed a different meaning-namely, antigenic determinants of microorganisms might elicit an auto-immune response that harms the host. The concept of molecular mimicry is based on a structural similarity between a pathogen or metabolite and self-structures. The similarity could be expressed as shared amino acid sequences (linear or mimotope) or similar conformational structure between a pathogen and self-antigen. "Molecular mimicry" has become a very popular explanation for the frequent association of infection with auto-immune disease.

Vaccines against myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease mediated by antibodies to nicotinic acetylcholine receptor (AChR) interfering with the neuromuscular transmission. Experimental autoimmune MG serves as an excellent animal model to study possible therapeutic modalities for MG. This review will focus on the different ways to turn off the autoimmune response to AChR, which results in suppression of myasthenia. This paper will describe the use of fragments or peptides derived from the AChR, antigen-presenting cells and anti-T cell receptor antibodies, and will discuss the underlying mechanisms of action. Finally, the authors propose new promising therapeutic prospects, including treatment based on the modulation of regulatory T cells, which have recently been found to be functionally defective in MG patients.