Background No single biomarker, suited for SLE diagnosis verification, have been found among a great number of candidates, and the oldest one, anti-dsDNA antibodies, remains to be suggested as most appropriate test. Native DNA and nucleoproteins are fairly unstable antigens, and its single usage in immunoassays, including ELISA, seems to be unreasonable. DNase I is a low-priced and widespread tool for DNA analysis, and its epitopes are quite stable. We are to assess validity and diagnostic efficiency of evaluation of serum anti-DNase I antibodies using enzyme immobilized on reusable magnetic polyacrylamide beads.

Purpose Comparative assessment of discrimination accuracy between SLE and other autoimmune rheumatic diseases by means of anti-DNase I antibodies testing.

Methods The research was carried out in agreement with the WMA Declaration of Helsinki principles after approval of the local Committee on Medical Ethics. All the patients signed the informed consent. 54 patients with verified SLE and 52 controls with verified diseases other than SLE (RA, systemic scleroderma, systemic vasculitis, idiopathic inflammatory myopathies, Sjogren’s disease) were included in the study. SLE diagnosis was verified using EULAR/ACR classification criteria (2019). 44 healthy volunteers were used as a reference group. Serum anti-DNase I antibody concentration was measured by modified ELISA test with DNase I immobilized on the magnetic polyacrylamide beads. The beads were synthesized using our original technique, and modified ELISA was performed as published previously.¹ Antibody concentrations were expressed as relative optical density units (ODU). Anti-DNA antibodies were measured by conventional ELISA. Results were expressed as means (95% confidence intervals). Differences were considered significant when p<0.05.

Results Anti-DNase I antibodies were detected in 35 (64.8%) SLE and 8 (15.4%) control patients. Average anti-DNase I concentration for SLE group was 0.079 (0.033–0.125), in the control group it was 0.063 (0.019–0.107) ODU (p>0.05). Optimum cutoff level between SLE patients and non-SLE autoimmune diseases (0.057 ODU) was equal to the lower limit of positive test results. Sensivity and specificity of the modified anti-DNase I ELISA were 64.74 (53.09–76.39) and 85.01 (72.95–97.07)%, respectively. Positive LR for this test was 4.21, and negative LR was 0.42. The area under anti-DNase I ROC curve had reached 0.774 and there was no significant difference between this AUC and the anti-dsDNA AUC.

Conclusion For the discrimination between SLE and commonly seen autoimmune rheumatic diseases diagnostic accuracy of the anti-DNase I antibodies test is high, being closely equal to the present reference standard, anti-dsDNA assay.

References

1. Gontar IP, Simakova ES, Trofimenko AS, Zborovskaya IA. An approach for removal of DNA-containing immune complexes from blood using composite sorbent. Patent RU2441674 (2010) [in Russian].