Evaluation of indirect immunofluorescence assay in patients with autoimmune diseases

Antinuclear antibodies (ANA) are the hallmark of autoantibody production in autoimmune disease. ANA are directed against components of the cell nuclei such as DNA, histones, nucleoli and ribonucleoproteins. ANA detected by indirect immunofluorescence (IIF) is the method of choice and is regarded as the gold standard technique. 100 patients with autoimmune disease attending a tertiary care hospital at Chennai, India and ten healthy controls were included in the study. Detailed clinical, serological and biochemical analysis were done. Blood samples were analyzed for ANA by IIF using in-house mouse liver and in-house HEp-2 cell line substrate. The cells showing apple green fluorescence and a definable nuclear staining pattern were taken as positive and the intensity of fluorescence graded from + to ++++ in serial dilutions of the sera. IIF patterns like homogeneous (solid) rim (peripheral), speckled and nucleolar patterns were observed. ANA positivity by IIF for SLE is 92.7 and 97.4% on mouse liver and HEp-2 cells, respectively. Specificity of ANA by IIF is 80 and 90% for mouse liver and HEp-2 cell substrate, respectively. Although, many commercial assays are available for the detection of ANA, IIF by in-house methods still holds good and is justified in this research work.   Key words: Autoantibodies, indirect immunofluorescence, antinuclear antibodies, systemic lupus erythematosus (SLE).