Anti-Mi-2 Antibody (Anti-Mi2)

Antibodies to Mi, an antigen in calf thymus extract, have been demonstrated by complement fixation inhibition in polymyositis (PM) and dermatomyositis (DM) sera but not in the sera of individuals without myositis. The original Mi reference serum defined 2 precipitating antibodies, using immunodiffusion (ID). Anti-Mi-1 was not active in complement fixation. Mi-2 antigen was purified by immuno-affinity chromatography. An enzyme-linked immunosorbent assay (ELISA) to measure Mi-2 antibody, using this antigen, was used to test the sera of 139 myositis patients: 52 had DM and 87 had PM. Control sera from 35 normal subjects and 93 patients with other connective tissue diseases were also tested. Only 13 sera were considered definitely positive for anti-Mi-2. All were from patients who had myositis, 11 of whom had DM. Only DM sera had anti-Mi-2 by ID, and all sera with anti-Mi-2 by ID were positive by ELISA.