Detection of Anti-Ssa Antibodies by Indirect Immunofluorescence (Clinical Immunology‪)‬

Anti-SSA antibodies are clinically important anti-nuclear antibodies in patients with systemic rheumatic diseases. These antibodies are found in ~60% of patients with Sjogren syndrome, in ~30% of patients with systemic lupus erythematosus, in a majority of patients with sub-acute cutaneous lupus, and in the neonatal lupus syndrome (1,2). They are also found in 5-8% of patients with rheumatoid arthritis (2). In many clinical laboratories, the initial screening test for the detection of anti-nuclear antibodies in general, and anti-SSA antibodies in particular, is indirect immunofluorescence using HEp-2 cells. The HEp-2 cell line is more sensitive than rodent tissue for the detection of anti-SSA antibodies (3) and has become the standard substrate for the nuclear antibody test. There are many commercial suppliers of HEp-2 substrates, but production techniques vary and there are no international guidelines on culture condition, fixation, and drying. Much of the discussion about the quality of the HEp-2 substrates has concentrated on how well the SSA antigen is preserved. SSA is present in low abundance, and diffusion of the antigen from the nucleus during fixation and subsequent sample preparation can occur (4). Ethanol and methanol fixation may cause denaturation and leaching of SSA to the cytoplasm (5). Therefore, acetone fixation of the HEp-2 substrate slides has been recommended (6).