Treg abnormalities have been observed, mostly in patients with psoriasis, including decreased expression of CD39 and CD7420, increased expression of IL-6Rα21, reduced suppressive capacity15,22–24, chemotactic deficiency25 and the enhanced propensity to differentiate into cells that produce interleukin (IL)-17–the hallmark cytokine of psoriatic disease15. Here, IL17A is linked to psoriasis.