Affiliations 

  • 1 Universiti Putra Malaysia
  • 2 Institute for Medical Research
MyJurnal

Abstract

Introduction: Systemic lupus erythematosus (SLE) has a broad spectrum of clinical presentations. The diagnosis of SLE remains a challenge and largely depends on the presence of several serum autoantibodies including anti-nuclear antibody (ANA), anti-double-stranded DNA antibody (anti-dsDNA) and anti-Smith antibody (anti-Sm). ANA, a highly sensitive but not specific marker is used for SLE screening Anti-dsDNA and anti-Sm are SLE-specific biomarkers but has lower sensitivity of 80% and 30% for SLE, respectively. However, it is noted that there are SLE patients who are persistently negative for SLE-specific autoantibodies. Anti-dsDNA and anti-Sm were reported to be negative in up to 51.2% and 62.4% of SLE, respectively. This limitation can lead to misdiagnosis and halter proper treatment to SLE patients. Previous studies have suggested that cell membrane DNA (cmDNA) can act as a specific target for the autoantibodies in SLE patients. Autoantibodies towards cmDNA (anti-cmDNA) were reported to have promis-ing value as a reliable biomarker for SLE. In this study, we would like to determine the usefulness of anti-cmDNA in diagnosing SLE as compared to the standard SLE-specific autoantibodies. Methods: Serum samples from 83 SLE patients, 86 other connective tissue diseases and 61 healthy subjects were included in this study. The other connec-tive tissue diseases include samples from 10 Sjogren’s syndrome, 56 rheumatoid arthritis, 12 scleroderma and eight mixed connected tissues disease (MCTD) patients. All samples were analysed by indirect immunofluorescence (IIF) technique using Raji cells as substrate to detect the presence of anti-cmDNA. Anti-cmDNA was reported as positive if there was presence of a fluorescent ring, either continuous or punctate. Sera from SLE patients were also tested for anti-dsDNA and anti-Sm antibodies by using enzyme-immunoassays. Results: Anti-cmDNA positivity was highest in SLE (55.4%) than in other connective tissue diseases (9.3%) and healthy subjects (0%). Anti-cmDNA was 100% spe-cific at differentiating SLE from healthy subjects and 90.7% specific at differentiating SLE from other connective tissue diseases. There was no difference in the sensitivity (55.4%) of anti-cmDNA at differentiating SLE from both groups. Anti-cmDNA were present in 46 SLE samples negative for standard SLE-specific autoantibodies. It was detected in 11 (42.3%) of anti-dsDNA, 23 (63.9%) of anti-Sm and 8 (12.9%) of both anti-Sm and anti-dsDNA negative samples. Conclusion: The high specificity of anti-cmDNA detection using IIF method makes it an excellent diagnostic tool for SLE. Anti-cmDNA is potentially a very useful biomarker for SLE with negative anti-dsDNA or/and anti-Sm antibodies.