To assess the added value of using a radioligand assay (RLA) compared with ELISA to detect antibodies to SSA, SSB and RNP, and to analyse the correlation between autoantibody levels, B-cell biomarkers and disease activity.
Antibodies to SSA, SSB and RNP were assessed in 127 patients with primary Sjögren syndrome (pSS) using an RLA and ELISA. In parallel, measures of B-cell activation were determined including serum levels of B-cell-activating factor of the tumour necrosis factor family or BLyS (BAFF).
RLA was more sensitive than ELISA for the detection of antibodies to SSB (54% of positive samples versus 37%, respectively) and antibodies to RNP (9% vs 3%). No difference was seen for the sensitivity of detection of antibodies to SSA. Anti-SSA and anti-SSB levels were correlated with both techniques. Mean levels of antibodies to SSA were significantly higher in patients presenting antibodies to both SSA and SSB than in those exhibiting antibodies to SSA only (RLA: mean (SEM) anti-SSA levels 2343 (158) cpm vs 1348 (286) cpm, respectively, p = 0.02; ELISA: 6.8 (0.8) vs 3.8 (0.4), respectively, p = 0.003). Levels of antibodies to SSA and SSB significantly correlated with those of circulating BAFF (r = 0.4, p = 0.004 and r = 0.6, p<0.001, respectively) and with B-cell biomarkers, including levels of gammaglobulins, beta(2) microglobulin and rheumatoid factor.
RLA allowed a quantitative and more sensitive detection of antibodies to SSB and RNP in pSS. Quantitative assessment of autoantibodies might disclose a biomarker of disease activity and enable further insight into the pathogenesis of the spreading of the autoantibody response.