Udey M C
Dermatology Branch, National Cancer Institute, Bethesda, MD 20892-1908, USA.
Clin Exp Immunol. 1997 Jan;107 Suppl 1:6-8.
Langerhans cells represent the epidermal contingent of a family of potent accessory cells termed 'dendritic cells'. Langerhans cells (and perhaps related cells in the dermis) are thought to be required for immune responses directed against foreign antigens and neoantigens that are encountered in skin. The 'life cycle' of the Langerhans cell is characterized by at least two distinct stages. Langerhans cells in epidermis (the 'sentinels') can ingest particulates and process antigens efficiently, but are weak stimulators of unprimed T cells. In contrast, Langerhans cells that have been induced to migrate to lymph nodes after contact with antigen in epidermis (the 'messengers') are not phagocytic and have limited antigen-processing capabilities, but are potent stimulators of naïve T cells. If Langerhans cells are to fulfil both their 'sentinel' and 'messenger' roles, they must be able to persist in epidermis for considerable periods, and also be able to exit epidermis in a controlled fashion after exposure to antigen. Thus, regulation of Langerhans cell-keratinocyte adhesion represents a key control point in Langerhans cell trafficking and function. Langerhans cells express E-cadherin, a homophilic adhesion molecule that is prominently represented in epithelia. Keratinocytes also express this adhesion molecule, and E-cadherin clearly mediates adhesion of murine Langerhans cells to keratinocytes in vitro. We presume that E-cadherin is involved in the localization of Langerhans cells in epidermis. Murine thymocytes also express E-cadherin early in the course of their development, and it is likely that E-cadherin plays an as yet uncharacterized role in thymocyte-thymic epithelial cell adhesion and in T-cell development. Recently, it has also been demonstrated that some cutaneous T-cell lymphoma cell lines are E-cadherin+, so E-cadherin may also mediate clinically important leucocyte-epithelial interactions in disease states.
朗格汉斯细胞是一类强大的辅助细胞（称为“树突状细胞”）家族的表皮成员。朗格汉斯细胞（以及真皮中可能相关的细胞）被认为是针对皮肤中遇到的外来抗原和新抗原的免疫反应所必需的。朗格汉斯细胞的“生命周期”至少有两个不同阶段。表皮中的朗格汉斯细胞（“哨兵”）能够有效摄取颗粒并处理抗原，但对未致敏T细胞的刺激较弱。相比之下，在表皮中接触抗原后被诱导迁移至淋巴结的朗格汉斯细胞（“信使”）不具有吞噬作用，抗原处理能力有限，但却是未成熟T细胞的强大刺激物。如果朗格汉斯细胞要同时履行其“哨兵”和“信使”的职责，它们必须能够在表皮中持续存在相当长的时间，并且在接触抗原后能够以可控的方式离开表皮。因此，朗格汉斯细胞与角质形成细胞黏附的调节是朗格汉斯细胞迁移和功能的关键控制点。朗格汉斯细胞表达E-钙黏蛋白，这是一种在上皮细胞中显著表达的同种型黏附分子。角质形成细胞也表达这种黏附分子，并且E-钙黏蛋白在体外明显介导小鼠朗格汉斯细胞与角质形成细胞之间的黏附。我们推测E-钙黏蛋白参与朗格汉斯细胞在表皮中的定位。小鼠胸腺细胞在其发育过程早期也表达E-钙黏蛋白，并且E-钙黏蛋白可能在胸腺细胞与胸腺上皮细胞黏附以及T细胞发育中发挥尚未明确的作用。最近，还证明一些皮肤T细胞淋巴瘤细胞系是E-钙黏蛋白阳性，因此E-钙黏蛋白在疾病状态下也可能介导临床上重要的白细胞与上皮细胞之间的相互作用。
