Detecting anti-SSA and anti-SSB antibodies in routine analysis: a comparison between double immunodiffusion and immunoblotting.

Abstract

The aim of this study was to assess the performance of a commercially available procedure for detecting anti-Sjögren's syndrome A (anti-SSA) and anti-Sjögren's syndrome B (anti-SSB) antibodies by immunoblotting (IB) and compare it with double immunodiffusion (DID). We also studied the clinical significance of these profiles in a series of unselected anti-SSA positive patients. Serum samples from 534 patients that were positive on an immunofluorescent screening test using HEp-2 cells were analysed for anti-SSA and anti-SSB antibodies by DID and IB (Biolab Anablot System II), and the results on anti-SSA antibodies were confirmed by an enzyme-linked immunosorbent assay (ELISA). Fifty-five serum samples were found to be positive for anti-SSA antibodies. Among these, 24 were anti-SSA negative by IB but positive by DID and ELISA ('non-blotter sera'), whereas only three serum samples were anti-SSA negative by DID but positive by IB and ELISA. Of the 18 anti-SSB positive serum samples, eight were negative by DID. All the serum samples that were anti-SSB positive by DID were also positive by IB. Anti-SSB antibodies showed a significant association with eye dryness and leucopenia. Anti-52 kDa SSA antibodies were associated with anti-SSB antibodies but showed no significant association with sicca symptoms, while anti-60 kDa SSA antibodies were associated with lower rates of leucopenia. The 'non-blotter' profile showed no significant association with any clinical parameter. IB is less sensitive than DID for detecting anti-SSA antibodies but more sensitive than DID for detecting anti-SSB antibodies. The determination of anti-SSA immunoblotting profiles in patients positive for anti-SSA antibodies by DID does not significantly improve the clinical usefulness of this test. As expected, anti-SSB antibodies were associated with clinical features of Sjögren's disease. Non-blotting (probably conformational) anti-SSA antibodies did not show any further association with clinical parameters and seem to have no clinical relevance.