CD4 and systemic lupus erythematosus: DNA hypomethylation in CD4+ T cells and B cells is a major factor contributing to SLE pathogenesis and the degree of hypomethylation is correlated with the disease activity (Javierre et al., 2010; Garaud et al., 2011; Long et al., 2016a; Wu et al., 2016a; Karagianni and Tzioufas, 2019).