Methotrexate, but not narrowband ultraviolet B radiation, suppresses interleukin-33 mRNA levels in psoriatic plaques and protein levels in serum of patients with psoriasis.

Interleukin (IL)-33 can function both as a conventional cytokine and as a nuclear factor regulating gene transcription. IL-33 expression is strongly upregulated in the nucleus of keratinocytes and serum of patients with psoriasis. However, the role of IL-33 in psoriasis is unclear, and IL-33 expression in the lesional psoriatic skin after conventional systemic treatments has not been investigated. In this study, we aimed to compare IL-33 mRNA in patients' lesional skin samples and IL-33 protein expression in patients' serum before and after treatment with methotrexate (MTX) and narrowband ultraviolet B (NB-UVB). IL-33 mRNA levels in lesional skin and IL-33 protein levels in serum were downregulated after treatment with MTX. Results revealed a significant decrease in IL-33 protein expression (P = 0.028). IL-33 expression increased after NB-UVB treatment. IL-33 production is associated with inflammatory skin in psoriasis, possibly through its cytokine function. However, high expression of IL-33 after NB-UVB treatment suggests the occurrence of unknown functions to alleviate psoriatic lesions without IL-33 involvement.