中文摘要：

朗格汉斯细胞是位于皮肤表皮的组织特异性不成熟树突细胞，其感知、传递外界环境的信号刺激并指导后续的免疫应答。早期研究显示，朗格汉斯细胞具有强大的诱导免疫应答的能力，在启动T细胞特异性免疫应答中起着重要的作用。而最近的一系列研究提示，朗格汉斯细胞的主要作用可能是诱导免疫耐受，其机制可能与特异性T细胞的清除、调节性T细胞的产生、协同刺激因素等相关。因此，朗格汉斯细胞不仅是免疫反应的哨兵，更是人体皮肤环境平衡的维护者。

英文摘要：

Langerhans cells （LCs） are tissue-specific immature dendritic cells located in the epidermis of skin. LCs sense, capture, process and present external stimuli and initiate subsequent immune responses. Previous researches mainly focused on the function of LCs to promote immune response, showing that LCs have potent ability to induce immune reaction by mediating T cell immune responses. However, recent studies have indicated that LCs can also induce immune tolerance, which might be related to the elimination of specific T cells, generation of regulatory T cells, production of co-stimulatory molecules, etc. Thus, LCs are not only a sentry of immune responses, but also a maintainer of skin environment homeostasis.