Suppression of Experimental Autoimmune Myasthenia Gravis by Intravenous Immunoglobulin and Isolation of a Disease-Specific IgG Fraction

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.

IVIg-mediated inhibition of antigen presentation: predominant role of naturally occurring cationic IgG

The infusion of high doses of intravenous immunoglobulins (IVIg) produce anti-inflammatory effects in a diversity of autoimmune disorders. The need for such high doses suggests that only a small fraction of IgG is responsible for the anti-inflammatory effects. We recently showed that IVIg was internalized in APCs to compete with antigens for loading on MHC II molecules, leading to reduced antigen-specific T cell responses. Here we show that highly cationic IgG molecules present in IVIg are internalized more efficiently than IVIg in mouse P388D1 cells. We also show that the increased internalization correlates with the extent of inhibition of antigen presentation. Chemically cationized IVIg similarly showed improved internalization and inhibition of antigen presentation properties compared to IVIg. These observations suggest that highly cationic IgG are important mediators of the anti-inflammatory effects of IVIg resulting from inhibition of antigen presentation, such as the reduction in T cell activation and autoantibody production.