IL17A and psoriasis: The immunological basis for psoriasis development involves both innate and adaptive immune arms.54,56–60 Notably, the adaptive response is primarily T-cell driven with major involvement of activated type 1, type 17 and type 22 responses, plus dysfunction of regulatory T cells.54,55 Of the interleukin (IL)-17 subtypes, IL-17A and IL-17F have most notably been shown to be increased in both the blood and lesional skin compartments of patients with psoriasis.55,61,62