The dark side of regulatory T cells in psoriasis.

Psoriasis is a hereditary disease elicited by chronic activation of cutaneous T cells. Delineating the mechanistic interplay of the cell subsets involved is key to developing the next generation of effective treatments. In this issue, Bovenschen et al. report that regulatory T cells maintain a fine balance between the transcription factors Foxp3 and RORγt. In patients with psoriasis, Tregs readily turn into IL-17-expressing cells, thus potentially perpetuating the inflammatory process that characterizes the disease. Results demonstrating that the histone/protein deacetylation inhibitor trichostatin A can block this conversion suggest that an epigenetic modification may underlie regulatory T-cell plasticity.