In psoriasis-affected patients for example, PDE4 has been shown to be expressed in all inflammatory cells involved in the pathophysiologic processes of this disease, including the production of cytokines such as TNF-α, IL-12, and IL-23 by antigen-presenting cells, and the synthesis of IL-2, IL-5, and IFN-γ by T cells [68]. Here, PDE4A is linked to psoriasis.