Comparison and identification of autoimmune antigens in seropositive and seronegative myasthenia gravis

Abstract

Myasthenia gravis (MG) was the first autoimmune disorder of the Peripheral Nervous System to be characterized. This disease is generally cause by autoantibodies that bind to the nicotinic acetylcholine receptors (AChR) at the post-synaptic muscle membrane. However, about 15% of patients do not have detectable levels of this antibody and are diagnosed to have seronegative myasthenia gravis (SNMG). Previous research in this lab has focused on autoimmune rippling muscle disease (ARMD), which has been reported to appear prior to the onset of (MG). Autoantigens have been characterized through the immunoscreening of a human skeletal muscle cDNA expression library using sera from patients with seropositive myasthenia gravis (SPMG) and (SNMG). SIS-PAGE analysis and Western blot studies have been carried out to better understand these target proteins. The patient's IgG and IgM autoantibodies were used to identify three unique muscle proteins. One of the three muscle proteins was titin-isoform (N2A). Titin is a large well known protein that is found in skeletal muscle. The protein extends from the Z line to the M line of the sarcomere. Titin provides passive tension to the muscle and acts as a template for normal muscle formation. Previous research performed in the lab has shown that the ARMD patients' sera also bound to titin-isoform (N2A). The Western blots of both the ARMD and the SPMG sera showed a unique doublet at about 123kDa. and 140kDa. The significance of this study is that the SPMG titin sequence fell in the Main Immunogenic Region (MIR) of the muscle protein. This region is believed to play a possible role in myasthenia gravis. Future studies are aimed at 2DE proteomic comparative analysis to help understand the connection between ARMD and SPMG.