Since VEGF-A upregulates CXCR4 in cultured human endothelial cells [16], and since elevated mRNA levels of both SDF-1 and CXCR4, as well as elevated SDF-1 protein levels, have been found in lesional psoriatic skin [21]–[23], we hypothesized that the SDF-1/CXCR4 axis might play a potential role in the pathogenesis of chronic inflammatory skin diseases including psoriasis. The gene discussed is CXCL12; the disease is psoriasis.