IL9 and psoriasis: A growing body of evidence has suggested that the RNA expression of both p40 and p19 increases greatly in psoriatic lesions, while the expression of p35 mRNA remains largely unchanged.50,51 The level of IL-23 protein can be greatly elevated in psoriatic lesions compared to unaffected skin.50 Thus, it can be inferred that the pathogenesis of psoriasis is related to IL-23 rather than IL-12.