RESUMO
BACKGROUND: Systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) are multisystemic autoimmune diseases with multifactorial nature. Considering the limitations of the current conventional serological tests for the diagnosis of these diseases, researchers strive to find more new valid biomarkers. METHODS: Sixty-nine patients with SLE, 63 patients with RA, and 71 healthy controls were recruited to evaluate the methylation level of interferon-induced protein 44-like (IFI44L) promoter. Quantitative methylation of the promoter region of the IFI44L gene was measured in extracted DNA of peripheral blood mononuclear cells (PBMCs) with methylation-quantification endonuclease-resistant DNA (MethyQESD) method. RESULTS: Our findings unveiled a drastic hypomethylation of IFI44L promoter in SLE and RA patients compared with healthy volunteers (mean: 40.23% ± 64.54%, 35.19% ± 24.09%, and 71.98% ± 23.83%, respectively; P < 0.001 for both SLE and RA). In comparison between SLE and RA patients with the control group, IFI44L promoter methylation had a sensitivity of 81.15% and 84.12%, respectively, and specificity was 76.05%. The promoter methylation level was not meaningfully different between SLE and RA patients (P = 0.267). Moreover, our analysis revealed that the methylation level of the IFI44L promoter was not significantly different between SLE disease activity and renal involvements (P > 0.05). While RA patients with a higher concentration of CRP had a lower DNA methylation level (P = 0.023). CONCLUSION: The methylation level of IFI44L promoter was lower in PBMCs of Iranian patients with SLE and RA than that in the control group. Furthermore, DNA methylation level of the IFI44L promoter had a negative correlation with RA disease activity. However, there was not a significant association with the clinical characteristics of SLE.