Lupus develops when genetically predisposed people encounter environmental agents, such as ultraviolet light, silica, infections, and cigarette smoke, that cause oxidative stress, but how oxidative damage modifies the immune system to cause lupus flares is unknown. We previously showed that inhibiting DNA methylation in CD4+ T cells by blocking ERK pathway signaling is sufficient to alter gene expression, and that the modified cells cause lupus‐like autoimmunity in mice. We also reported that T cells from patients with active lupus have decreased ERK pathway signaling, have decreased DNA methylation, and overexpress genes normally suppressed by DNA methylation. This study was undertaken to test whether oxidizing agents decrease ERK pathway signaling in T cells, decrease DNA methyltransferase levels, and cause demethylation and overexpression of T cell genes similar to that found in T cells from patients with active lupus.

CD4+ T cells were treated with the oxidizers H₂O₂ or ONOO⁻. Effects on ERK pathway signaling were measured by immunoblotting, DNA methyltransferase 1 (DNMT‐1) levels were measured by reverse transcriptase–polymerase chain reaction (RT‐PCR), and the methylation and expression of T cell genes were measured using flow cytometry, RT‐PCR, and bisulfite sequencing.

H₂O₂ and ONOO⁻ inhibited ERK pathway signaling in T cells by inhibiting the upstream regulator protein kinase Cδ, decreased DNMT‐1 levels, and caused demethylation and overexpression of genes previously shown to be suppressed by DNA methylation in T cells from patients with active lupus.

Our findings indicate that oxidative stress may contribute to human lupus flares by inhibiting ERK pathway signaling in T cells to decrease DNMT‐1 and cause DNA demethylation.