Detection of Anti-SSA Antibodies by Indirect Immunofluorescence

Background: HEp-2 cells that overexpress the human 60-kDa SSA antigen have been used to improve sensitivity and specificity for the detection of anti-SSA antibodies by indirect immunofluorescence. We describe a survey on the detection of anti-SSA antibodies using a commercial substrate that overexpresses SSA.

Methods: The evaluation was done on 18 371 consecutive samples submitted to the laboratory for detection of anti-nuclear antibodies, from which 188 anti-SSA antibody-containing and clinically documented samples were obtained. The presence of anti-SSA antibodies produced a distinct bright speckled pattern with nucleolar staining in 10–20% of interphase cells. The identity of all anti-SSA antibodies was confirmed by dot-blot analysis.

Results:Samples containing anti-SSA antibodies were separated into three main groups: group I, distinctive SSA pattern and other nuclear staining (50%); group II, only the distinctive SSA pattern (29%); group III, nuclear staining but without the distinctive SSA pattern (21%). Anti-SSA antibodies with concurrent SSB antibodies were associated with group I, whereas anti-SSA antibodies with concurrent U1-RNP antibodies were associated with group III. Group I included mainly patients with Sjögren syndrome and systemic lupus erythematosus (SLE), whereas group III included patients with mixed connective tissue disease and SLE. Diseases not classically associated with the presence of anti-SSA antibodies were found in group II in >50% of the cases.

Conclusions: SSA-positive individuals were identified in a population selected on the basis of HEp-2000 positivity. Our study highlights diseases associated with anti-SSA antibodies and associations between the presence of the distinctive SSA pattern on HEp-2000 and some clinical conditions.