To determine the biochemical structure and antigenic components of Mi-2 autoantigen, the target of autoantibodies in 1520% of dermatomyositis patients.
Methods. Immunoprecipitation from 35S-labeled HeLa cell extract, immunoblotting, and purification from bovine thymus by immunoaanity chromatography.
Results. All 46 sera that had anti-Mi-2 autoantibodies demonstrated by immunodiffusion immunoprecipitated a major protein of -240 kd. Additional proteins of 200, 150, 72, 65,63, 50, and 34 kd appeared to be part of the antigen. Fractions of purified bovine Mi-2 with antigenic activity showed high molecular weight bands comparable with immunoprecipitated HeLa Mi-2. Twenty-four of 47 anti-Mi-2 positive sera reacted with the 240-kd protein by immunoblot against anti-Mi-2 immunoprecipitates.
Conclusion. Mi-2 antigen consists of multiple proteins, of which the 240-kd protein appears to be the major reactive component.
A series of autoantibodies to cellular antigens has been associated with dermatomyositis (DM) and polymyositis (PM). Several of these autoantibodies are considered to be myositis specific because they are found almost exclusively in conjunction with this disease (1-5). The best studied of these are the antibodies to aminoacyl-transfer RNA (tRNA) synthetases such as anti-Jo-1 (anti-histidyl-tRNA syn-