Yinxieling decoction ameliorates psoriasis by regulating the differentiation and functions of Langerhans cells via the TGF‐β1/PU.1/IL‐23 signal axis

Abstract Langerhans cells (LCs) play a critical role in skin immune responses and the development of psoriasis. Yinxieling (YXL) is a representative Chinese herbal medicine for the treatment of psoriasis in South China. It was found to improve psoriasis without obvious side effects in the clinic. Here we attempted to clarify whether and how YXL regulates the differentiation and functions of LCs in Imiquimod (IMQ)‐induced psoriasis in vivo and induced LCs in vitro. The Psoriasis Area Severity Index (PASI) score was used to evaluate the efficacy of YXL for IMQ‐induced psoriasis‐like mice. Flow cytometry was utilized to analyze the effects of YXL, to regulate the differentiation, migration, maturation, and antigen presentation of LCs. The results show that YXL significantly alleviated skin inflammation, as reduced in PASI score and classic psoriasis characteristics in pathological sections. Although there was no effect on the proportion of total DCs in the skin‐draining lymph nodes, the expression of epidermal LCs and its transcription factor PU.1 were both markedly inhibited. LCs were also prevented from migrating from epidermal to skin‐draining lymph nodes and mature. In addition, the number of LCs carrying antigens in the epidermis increased, which suggested that YXL could effectively prevent LCs from presenting antigens. In vitro, YXL had a significant impact on inhibiting the differentiation of LCs. Further data showed that YXL decreased the relative expression of transforming growth factor‐β (TGFβ) messenger RNA (mRNA) and interleukin‐23 (IL‐23) mRNAs. Thus, YXL alleviates psoriasis by regulating differentiation, migration, maturation, and antigen presentation via the TGFβ/PU.1/IL‐23 signal axis.