The value and clinical application of autoantibodies against cell membrane associated DNA in systemic lupus erythematosus

Objective To determine the cut-off value of anti-cmDNA antibody in systemic lupus erythematosus(SLE) detected by indirect immunofluorescence assay (IIF) on human's B lymphoma cell line Raji, and to explore the diagnostic value of anti-cmDNA antibody in SLE. Methods We included 129 patients with SLE. As the control group, we included 69 patients with other rheumatic diseases and 50 healthy subjects. IIF was used to detect the anti-cmDNA antibody. Different threshold levels (1∶10, 1∶20, 1∶40, 1∶80, 1∶160, 1∶320, 1∶640, 1∶1 280) for positive results were calculated by the areas under the receiver operating characteristic curve (ROC) area under curve (AUC). By comparing the AUC of all titers of anti-cmDNA anti-body in SLE, the best diagnosis cut-off value for SLE was determined. Then anti-cmDNA antibody was tested in 435 patients with SLE, 192 patients with other rheumatic diseases, and 50 healthy blood donors. The diagnostic value of anti-cmDNA antibody in SLE was evaluated. At the same time, ANA and anti-dsDNA were measured by IIF. Anti-Sm was measured by immuno-double diffusion and Western blotting. AnuA was measured by enzyme linked immunosorbent assay. T-test, four-table χ2 test and McNemar χ2 test were used for statistical analysis. Results ① By comparing the AUC of all titers of anti-cmDNA antibody in SLE, the best diagnosis cut-off value for SLE was determined as 1:40 (AUC=0.643). ② The sensitivity and specificity of anti-cmDNA antibody for SLE was 72.9% and 90.7% respectively. The AUC of anti-cmDNA, anti-dsDNA, anti-Sm, AnuA and ANA for SLE was 0.836, 0.746, 0.617, 0.845 and 0.762 respectively. The sensitivities of anti-dsDNA, anti-Sm and AnuA were much higher when combined with anti-cmDNA than those detected individually (χ2=109.20, 243.28, 12.57; P<0.05). Conclusion We concluded that the best diagnosis cut-off value of anti-cmDNA for SLE has been determined as 1∶40. Anti-cmDNA antibody has high sensitivity and specificity in SLE. Combined anti-cmDNA and other autoantibodies might further improve the diagnostic sensitivity in SLE. Key words: Lupus erythematosus, systemic; Diagnosis; Autoantibodies; Anti-cmDNA antibody; Cell line Raji