Effect of methotrexate on serum levels of IL-22 in patients with psoriasis

Interleukin-22 (IL-22) is the effector molecule of T-helper subset 22 (Th-22) lineage that promotes keratinocyte proliferation and dermal inflammation in psoriasis. Methotrexate is widely used as a first-line treatment in moderate to severe psoriasis. Methotrexate inhibits inflammatory and cytokinetic processes via various mechanisms, but the relevance of these to psoriasis is limited and whether methotrexate is specifically able to down-regulate Th22 cytokines is unknown. To determine if methotrexate reduces IL-22 in cases of psoriasis. Nineteen patients with moderate to severe psoriasis were given methotrexate 15 mg per week for up to 12 weeks. Serum levels of IL-22 were determined by enzyme-linked immunosorbent assay (ELISA) before and after treatment. Eleven of 19 patients (57.8%) achieved a 75% PASI score reduction. IL-22 levels were significantly higher in untreated psoriasis patients (56.63 ± 60.73 pg/mL) than in controls (12.58 ± 12.59 pg/mL). Methotrexate significantly reduced serum levels of IL-22 in psoriasis patients to 5.91 ± 7.97 pg/mL (p<0.001). Moreover, there was a significant positive correlation between IL-22 levels and PASI (r=0.63, p=0.004). Methotrexate significantly reduces serum IL-22 levels in cases of psoriasis. This is a novel mechanism by which methotrexate acts in the treatment of this disease.