Use of a commercial line blot assay as a screening test for autoantibodies in inflammatory myopathies

Aims To evaluate the clinical utility of a commercial immunoblot assay for the detection of myositis-specific autoantibodies. Methods Serum samples from 153 myositis patients and 77 disease controls were investigated. The commercial Euroline assay with seven autoantigens (Mi-2, Ku, PM-Scl, Jo-1, Pl-7, Pl-12 and SSA/Ro-52) was used according to the manufacturer´s instructions, and supplemented with an anti-SRP strip. In a separate experiment analyses were performed at different temperatures. Results were recorded with densitometry. Results Anti-Jo-1 was found in 18 myositis and one systemic sclerosis patient. Antibodies against Mi-2 were found in 5 myositis patients, and eleven myositis patients had antibodies against PM-Scl. Four myositis patients showed anti-Pl-7 reactivity, whereas no patients had antibodies against Pl-12. Anti-Ku antibodies were found in 4 myositis and 2 primary Sjögren´s syndrome patients. Anti-SRP was found in 8 myositis patients as well as in two disease controls. Antibodies against SSA/Ro52 ranged between 23–62% in all groups except juvenile dermatomyositis patients. Most autoantibody reactivities were clearly positive, only 11% (14/127) were borderline positive. Higher assay temperature increased antibody reactivities. Conclusions Except for anti-SSA/Ro-52 and anti-Ku the antibody reactivities were rather myositis-specific, supporting the use of this immunoblot assay. However, assay validation needs to be determined against other methods.