Lowered IL-37 gene expression and elevated IL-37-producing tissue-resident immune cells in psoriasis lesional biopsies

Psoriasis is an immune cell-dependent chronic autoimmune skin disorder. Interleukin 37 (IL-37) is a cytokine belonging to the IL-1 family that shows anti-inflammatory and protective effects in various mouse models of psoriasis. Even though various animal models are used to investigate the pathogenic mechanisms of psoriasis, human clinical studies are still needed to make up for the deficiencies, as animal models generally do not exhibit the complex phenotypic features of human psoriasis. Our study aims to demonstrate the relationship between IL-37-producing tissue-resident immune cells with the pathogenesis of psoriasis. The present study was performed on 28 psoriasis patients and 17 healthy volunteers. The ability of anti-inflammatory cytokine IL-37 to impede inflammation and regulate metabolic pathways was assessed by real-time quantitative polymerase chain reaction. Finally, immunofluorescence double staining for CD4⁺IL-37b⁺, CD68⁺IL-37b⁺, and (forkhead box protein P3) Foxp3⁺IL-37b⁺ was performed. The proportion of CD4⁺IL-37b⁺ T cells, CD68⁺IL-37b⁺ macrophages, and Foxp3⁺IL-37b⁺ T regulatory (Treg) cells was significantly increased in the psoriasis group compared to the control group. IL-37 gene expression was downregulated in psoriasis when contrasted to the control group. Our findings disclosed that IL-37-producing tissue-resident immune cells might be involved in the pathogenesis of psoriasis, and thus may be a therapeutic target for individuals with psoriasis.