Bath Psoralen Plus UVA Therapy Suppresses Keratinocyte-Derived Chemokines in Pathogenetically Relevant Cells

Psoriasis is a chronic inflammatory proliferative skin disease involving various types of chemokines regulating immune cell migration, localization, and activation. Bath psoralen plus UVA (PUVA) treatment is an established phototherapy for psoriasis, but its effects on chemokine levels remain unknown. We investigated the levels of 22 serum chemokines in 20 patients with psoriasis first treated with bath PUVA therapy between 2007 and 2011 in a single center and analyzed the associations between the chemokines and disease severity (PASI) before and after therapy to investigate the mechanisms of action of bath PUVA therapy. Before bath PUVA therapy, the PASI scores correlated with the serum levels of CCL17 (r = 0.581), CCL18 (r = 0.462), CCL19 (r = 0.477), and CXCL16 (r = 0.524). After bath PUVA, the serum levels of CCL17, CCL22, CXCL1, and CXCL9 were significantly decreased. Heatmap clustering and network analysis based on statistically significant Spearman correlations among the chemokines showed distinctive changes in the chemokine signature. Our findings revealed that the levels of several chemokines correlated with the disease state of psoriasis. Furthermore, bath PUVA therapy reduced the secretion of keratinocyte-derived chemokines that induce the migration of immune cells important for psoriasis pathogenesis, partly revealing the mechanism of the therapeutic activity.