IL17A and psoriasis: The infiltration of IL-17A–positive CD4+ T cells, γδ T cells, and neutrophils was observed in the skin at the experimental endpoint (Fig 3G–I) and in human psoriasis (Kryczek et al, 2008; Cai et al, 2011; Dyring-Andersen et al, 2017), suggesting a critical role of the damaged skin–derived immune cells in systemic IL-17A production.