TCR⁺CD3⁺CD4^-CD8^- effector T cells in psoriasis

The autoimmune/inflammatory disorder psoriasis is characterized by keratinocyte proliferation and immune cell infiltration of the skin. TCR⁺CD3⁺CD4^-CD8^- "double negative" (DN) T cells can derive from CD8⁺ T cells through the down-regulation of CD8. The inhibitory molecule programmed death (PD-)1 is expressed on activated T cells and plays a role in the maintenance of peripheral tolerance. A subset of DN T cells, characterized by the expression of PD-1, has recently been demonstrated to be self-reactive. We demonstrate that a majority of DN T cells exhibits effector memory phenotypes, express IFN-γ, and fail to proliferate. DN T cells from psoriasis patients are characterized by reduced DNA methylation of the IFNG gene and increased PD-1 expression. Furthermore, PD-1 positive DN T cells infiltrate the epidermis in psoriatic skin lesions. Our observations offer additional insight into the molecular pathophysiology of plaque psoriasis and show promise as potential disease biomarkers and/or therapeutic targets for future interventions.