CD8A and psoriasis: The efficacy of oral nystatin in reducing psoriasis symptoms (154–157) [oral nystatin is not absorbed and thus limited to killing fungi in the gut (163, 164)], the expression of αEβ7 integrin by CD8+ T cells in psoriatic lesions (165) (αEβ7 integrin is a marker of mucosal origin), and the triggering of psoriasis by vedolizumab (140, 141) suggest that some psoriasis cases may be caused by lymphocytes originating in the gut.