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

The aim of this study was to assess the performance of a commercially avail able procedure for detecting anti-Sjogren's syndrome A (anti-SSA) and anti- Sjogren's syndrome B (anti-SSB) antibodies by immunoblotting (IB) and compa re it with double immunodiffusion (DID). We also studied the clinical signi ficance of these profiles in a series of unselected anti-SSA positive patie nts. Serum samples from 534 patients that were positive on an immunofluores cent screening test using HEp-2 cells were analysed for anti-SSA and anti-S SB 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 an tibodies. 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 positi ve serum samples, eight were negative by DID. All the serum samples that we re anti-SSB positive by DID were also positive by IB. Anti-SSB antibodies s howed a significant association with eye dryness and leucopenia. Anti-52 kD a SSA antibodies were associated with anti-SSB antibodies but showed no sig nificant association with sicca symptoms, while anti-60 kDa SSA antibodies were associated with lower rates of leucopenia. The 'non-blotter' profile s howed no significant association with any clinical parameter. IB is less se nsitive than DID for detecting anti-SSA antibodies but more sensitive than DID for detecting anti-SSB antibodies. The determination of anti-SSA immuno blotting 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 Sjogren's d isease. Non-blotting (probably conformational) anti-SSA antibodies did not show any further association with clinical parameters and seem to have no c linical relevance.