Diagnostic accuracy and predictive value of extended autoantibody profile in systemic sclerosis

Systemic sclerosis (SSc) is a heterogeneous autoimmune disorder characterized by microvascular injury, fibrosis of the skin and other organs, and presence of antinuclear autoantibodies (ANA) with a prevalence varying from 80 to 98%. The ANA classically detected in SSc include anti-centromere (ACA) and anti-topoisomerase I (ATA), which are positive in 50-60% of the patients. Even if other autoantibodies, such as anti-fibrillarin (AFA), anti-RNA polymerase III (RNAP III), anti-PMScl, anti-Th/To, and anti-hUF/NOR-90, are almost specific for SSc, until recently they were not routinely looked for, since the techniques for their identification were not suitable for routine use. In recent years, the advances in the knowledge of the biochemistry and of the immunoreactive sites of the autoantigens led to the development of new immunoassays using recombinant proteins as autoantigens. We evaluated a new multiplex line immunoblot assay (LIA) for the simultaneous detection of 13 different SSc-associated autoantibodies, in a cohort of 210 SSc Italian patients. The sensitivity and the specificity of this assay were as follows: 30.5% and 97.3% for ACA (anti-CENP-B), 29.5% and 96% for ACA (anti-CENP-A), 20% and 99.3% for ATA, 5.7% and 99.3% for anti-RNAP III (RP-155), 5.2% and 100% for anti-RNP III (RP-11), 6.7% and 98% for anti-PMScl (PMScl-100), 10.9% and 93.3% for anti-PMScl (PMscl-75), 3.3% and 98.7% for anti-Th/To, 0.48% and 100% for AFA, 4.8% and 96.7% for anti-hUF/NOR-90, 4.7% and 96% for anti-Ku, 0.95% and 100% for anti-Platelet-Derived Growth Factor Receptor, and 18.1% and 50% for anti-Ro-52, respectively. These results, which are similar to those obtained in other studies using traditional techniques, show that the LIA assay can be considered a more rapid and a more practical method than immunoprecipitation assays for studying SSc-related antibodies in the diagnostic work-up of SSc patients.