Objectives Antigen-specific CD4⁺ T cells epigenetically modified with DNA methylation inhibitors overexpress genes normally suppressed by this mechanism, including CD11a, CD70, CD40L and the KIR gene family. The altered cells become autoreactive, losing restriction for nominal antigen and responding to self-class II major histocompatibility complex (MHC) molecules without added antigen, and are sufficient to cause a lupus-like disease in syngeneic mice. T cells overexpressing the same genes are found in patients with active lupus. Whether these genes are co-overexpressed on the same or different cells is unknown. The goal of this study was to determine whether these genes are overexpressed on the same or different T cells and whether this subset of CD4⁺ T cells is also present in patients with lupus and other rheumatic diseases.

Methods Multicolour flow cytometry was used to compare CD11a, CD70, CD40L and KIR expression on CD3⁺CD4⁺CD28⁺ T cells to their expression on experimentally demethylated CD3⁺CD4⁺CD28⁺ T cells and CD3⁺CD4⁺CD28⁺ T cells from patients with active lupus and other autoimmune diseases.

Results Experimentally demethylated CD4⁺ T cells and T cells from patients with active lupus have a CD3⁺CD4⁺CD28⁺CD11a^hiCD70⁺CD40L^hiKIR⁺ subset, and the subset size is proportional to lupus flare severity. A similar subset is found in patients with other rheumatic diseases including rheumatoid arthritis, systemic sclerosis and Sjögren's syndrome but not retroperitoneal fibrosis.

Conclusions Patients with active autoimmune rheumatic diseases have a previously undescribed CD3⁺CD4⁺CD28⁺CD11a^hiCD70⁺CD40L^hiKIR⁺ T cell subset. This subset may play an important role in flares of lupus and related autoimmune rheumatic diseases, provide a biomarker for disease activity and serve as a novel therapeutic target for the treatment of lupus flares.