A murine model of IMQ-induced psoriasis-like dermatitis clearly demonstrated that PD-1 deficiency accelerates infiltration of epidermal CD8 T cells with enhanced IFN-γ production of inflamed skin, and IFN-γ-stimulated keratinocytes produced an IFN-γ-inducible chemokine (CXCL9) for recruitment of T cells. This evidence concerns the gene CXCL9 and psoriasis.