TNF-α also acts synergistically with IL-17 to upregulate the expression of inflammatory genes implicated in psoriasis, including genes that encode key molecules in the molecular signature of psoriasis, such as psoriasin (S100A7), β-defensin, IL-8, chemokine (C-C motif) ligand 20 (CCL20), IL-23 (p19), and chemokine (C-X-C motif) ligand 1 (CXCL1) [19]. This evidence concerns the gene XCL1 and psoriasis.