Initiation of Autoimuunity in Myasthenia Gravis

Penn, Audrey

Abstract

We are studying mechanisms by which automimmunity is initiated in myasthenia gravis. D-penicillamine (D-Pen) in certain patients with rheumatoid arthritis initiates an immune response shown that individual humans and rabbits receiving long-term D-Pen exposure develop antibodies to D-Pen itself, as well as to AChR while strain C3H and A mice develop T cells which recognizes AChR after such exposure but only manifest antibodies after receiving one injection of AChR Serum from a few patients with D-Pen-MG has also reacted with a synthetic fragment peptide (179 to 191) which is coincident with the ligand binding site for AChR alpha chain. Cysteines 192, 193 form the disulfide most likely to be reduced by D-Pen. Accordingly we now plan to extend the studies of T cells from mice exposed to D-Pen chronically so as to assess whether or not they proliferate to D-Pen presented on other protein carriers or on other lymphoid cells; to investigate how T cell recognition of D- Pen proceeds to trigger B cells synthesis of AChR; to use the synthetic fragment peptide 179 to 191 and the longer version containing the reactive disulfide (179 to 196) to evaluate them as probable antigenic sites for T cells and antibody recognition. In D-Pen-MG patients, we will assess recognition by their T cells of AChR, D-Pen presented on AChR and on another protein carrier, also assess antibody and proliferative responses to the synthetic fragment peptides and assess their T cells for ability to augment anti-AChR synthesis by B cells in vitro. We also plan to continue investigations of the contribution of thymic myoid cells to the histopathology of the myofibrillar proteins) present normally in these cells. Over 80% myasthenics, especially with concurrent thymoma, have anti-myofibrillar antibodies detectable by ELISA and immunoblot. We can detect myoid cells using fluorochrome-labelled bungarotoxin, specific antibodies to human skeletal myosin and actin and autoantibodies (F(ab1)2). We are presently working to isolate Ia+ dendritic-macrophage cells from normal and myasthenic thymus so as to test their ability to present AChR and myofibrillar proteins to T cells or thymocyte-T cells. We plan to investigate the ability of cultured muscle from thymus or myoid cells to express Ia or induce presentation of muscle antigens to immune cells. We will investigate thymocytes from thymus glands bearing thymomas to evaluate whether or not are sensitized to muscle antigens and evaluate mechanisms that may trigger this.