Higher IL-9 Level is Associated with Psoriasis Vulgaris Complicated by Metabolic Syndrome

PURPOSE: The underlying pathophysiology linking psoriasis vulgaris (PV) and metabolic syndrome (MetS) is not fully understood. The present study aimed to investigate the serum level of interleukin (IL)-9 and tissue levels of IL-9 and its receptor in PV patients with MetS and analyze the correlation of IL-9 levels with psoriasis disease severity and MetS. METHODS: This study enrolled 75 PV patients with MetS, 57 PV patients without MetS, 20 healthy blood donors, and 7 healthy skin donors. Clinical, socio-demographic, and anthropometric data were obtained from all individuals. Fasting blood glucose, insulin, lipid profile levels, and serum levels of IL-9 and IL-17A were measured. The expression of IL-9 and its receptor in skin specimens in PV patients and healthy controls was determined using immunohistochemistry. Normal human epidermal keratinocytes were stimulated with five pro-inflammatory cytokines (tumor necrosis factor-α, oncostatin M, IL-22, IL-17A, and IL-1α) to establish a psoriatic keratinocyte model and subsequently treated with IL-9. Their mRNA levels of antimicrobial peptides and chemokines were measured using quantitative real-time polymerase chain reaction. RESULTS: Serum level of IL-9 and tissue levels of IL-9 and its receptor were upregulated in PV patients with MetS. IL-9 level was positively correlated to IL-17A level; however, no significant correlation of IL-9 level with psoriasis area severity index was observed. IL-9 level had a positive correlation with the presence of MetS and its components. Correspondingly, IL-9 level positively correlated with waist circumference, body mass index, homeostasis model assessment-insulin resistance, blood pressure, and triglyceride level and negatively correlated with high-density lipoprotein cholesterol level. Additionally, IL-9 stimulated the expression of antimicrobial peptides and chemokines in a psoriatic keratinocyte model. CONCLUSION: Our findings confirmed that higher IL-9 level is associated with PV complicated by MetS, suggesting that IL-9 may be a link between PV and MetS.