Systemic ALA‐PDT effectively blocks the development of psoriasis‐like lesions and alleviates leucocyte infiltration in the K14‐VEGF transgenic mouse

SummaryBackground Psoriasis is one of the most common immune-mediated chronic inflammatory skin disorders. In spite of significant advances in the treatment of psoriasis, more effective and safer therapeutic strategies are still needed. Photodynamic therapy (PDT) is a method of light treatment that is being used increasingly in the treatment of dermatological diseases. Aim To evaluate the therapeutic effects of systemic 5-aminolaevulinic acid (ALA)-PDT on psoriasis and to explore its potential mechanism of action. Methods We investigated the therapeutic effects of systemic ALA-PDT in K14-vascular endothelial growth factor (VEGF) transgenic homozygous mice, an animal model of psoriasis, which has many clinical and histopathological characteristics similar to those of human psoriasis. Using haematoxylin and eosin staining, immunohistochemistry and real-time quantitative PCR respectively, we assessed the changes in psoriasis-like lesions, cellular infiltration of T cells, dendritic cells (DCs) and neutrophils, and the mRNA expression of the inflammatory cytokines interleukin (IL)-17 and interferon (IFN)-γ in the lesions. Results Systemic ALA-PDT blocked the development of psoriasis-like lesions and moderately attenuated the histopathological changes in K14-VEGF transgenic mice. Furthermore, systemic ALA-PDT produced an obvious reduction in infiltration of T cells, CD11c+ DCs and neutrophils in psoriasis-like lesions. In addition, systemic ALA-PDT also significantly decreased the mRNA expression of IL-17 and IFN-γ. Conclusions We suggest that the mechanism of systemic ALA-PDT in this psoriasis-like model might be associated with selective damage to abnormal T helper (Th)1 and Th17 cells, and reduction of the inflammatory cytokines IL-17 and IFN-γ. These observations partly explain the potential mechanism of systemic ALA-PDT in psoriasis and other inflammatory skin diseases.