Specificity of anti-Scl-70 antibodies in scleroderma: increased sensitivity of detection using purified DNA topoisomerase I from calf thymus.

A large scale purification of DNA topoisomerase I from calf thymus was obtained using the combinations of 62% ammonium sulfate precipitation, Biorex 70, hydroxylapatite and phenylagarose chromatography. Silver staining of the preparation separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed 2 bands of apparent molecular weight of 70 and 60 kDa. Immunoblotting with a serum of anti-Scl-70 specificity also recognized both proteins. Anti-Scl-70 antibodies were detected in 24/32 (75%) patients with diffuse scleroderma by ELISA and 28/32 (87%) had the ability to neutralize the topoisomerase I activity. All of 14 sera with anticentromere antibodies did not react with DNA topoisomerase I by both assays. The presence of anti-Scl-70 antibodies remained disease specific despite the increase in sensitivity of both assays.