Immunopharmacology and inflammationPaeoniflorin inhibits imiquimod-induced psoriasis in mice by regulating Th17 cell response and cytokine secretion

Paeoniflorin (PF) is the main active ingredients of radix paeoniae rubra and radix paeoniae alba, which are used widely in Traditional Chinese Medicine. This study aimed to assess the capacity of PF to inhibit imiquimod (IMQ)-induced psoriasis. Mice treated with IMQ were divided into four groups and administered 240 mg/kg/day or 120 mg/kg/day of PF, 1 mg/kg/day of methotrexate (MTX), or normal saline intragastrically. Weight-matched mice treated with vaseline were used as controls. Morphology, structural features, keratinocyte proliferation and differentiation, inflammatory cell infiltration, levels of Th1/Th2/Th17/Treg cytokine mRNA, and phosphorylation of Th17 differentiation-related proteins were assessed. Mouse spleen cells were incubated under Th17 polarizing conditions, then with PF (2, 20, and 200 μg/ml) and cell viability, Th17 differentiation, and Th17 cytokines and the orphan nuclear receptor (RORγt) mRNA levels were assessed. PF alleviated IMQ-induced keratinocyte proliferation and inflammatory cell infiltration, and reduced mRNA levels of Th17 cytokines at day 4 and phosphorylation of Th17 differentiation-related proteins. However, 2, 20, or 200 μg/ml PF did not affect spleen cell viability, and 2 and 20 μg/ml PF reduced IL-17 secretion under Th17 polarizing conditions. Finally, 2 and 20 μg/ml PF inhibited mRNA expression of Th17 cytokines and phosphorylation of Stat3 in spleen cells under Th17 polarizing conditions. These results suggest that PF inhibits IMQ-induced psoriasis by regulating Th17 cell response and cytokine secretion via phosphorylation of Stat3.