Systemic lupus erythematosus (SLE) is an autoimmune disease that is characterized by lymphocytic infiltration and overproduction of autoantibodies, leading to significant morbidity and mortality. However, the pathogenesis of this disorder has not yet been completely elucidated. It has been reported that CD70, a B cell costimulatory molecule encoded by the gene TNFSF7 (tumor necrosis factor ligand superfamily member 7), is overexpressed in CD4+ T cells from patients with SLE due to the demethylation of its promoter. We aimed to investigate the expression patterns of MBD4 (methyl-CpG binding domain protein 4) in CD4+ T cells and its contribution to the pathogenesis of SLE by increasing CD70 expression through epigenetic regulation.,Our results showed that the expression of MBD4 was significantly decreased in CD4+ T cells from SLE patients. We verified that transfection of MBD4 siRNA into healthy CD4+ T cells upregulated expression of CD70 and decreased the methylation level of the CD70 promoter. Overexpression of MBD4 inhibited CD70 expression and enhanced the DNA methylation level of CD70 in CD4+ T cells of SLE patients.,Our results indicated that downregulation of MBD4 contributed to overexpression and hypomethylation of the CD70 gene in SLE CD4+ T cells. This modulation of MBD4 may provide a novel therapeutic approach for SLE.