Division of Infection and Immunity, University College London, London, UK.
Immunology. 2020 Jun;160(2):116-125. doi: 10.1111/imm.13152. Epub 2019 Dec 4.
The skin is the outermost layer of the body with an extensive surface area of approximately 1·8 m , and is the first line of defence against a multitude of external pathogens and environmental insults. The skin also has important homeostatic functions such as reducing water loss and contributing to thermoregulation of the body. The structure of the skin and its cellular composition work in harmony to prevent infections and to deal with physical and chemical challenges from the outside world. In this review, we discuss how the structural cells such as keratinocytes, fibroblasts and adipocytes contribute to barrier immunity. We also discuss specialized immune cells that are resident in steady-state skin including mononuclear phagocytes, such as Langerhans cells, dermal macrophages and dermal dendritic cells in addition to the resident memory T cells. Ageing results in an increased incidence of cancer and skin infections. As we age, the skin structure changes with thinning of the epidermis and dermis, increased water loss, and fragmentation of collagen and elastin. In addition, the skin immune composition is altered with reduced Langerhans cells, decreased antigen-specific immunity and increased regulatory populations such as Foxp3 regulatory T cells. Together, these alterations result in decreased barrier immunity in the elderly, explaining in part their increased susceptiblity to cancer and infections.
皮肤是人体的最外层，拥有约 1.8 平方米的广阔表面积，是抵御众多外部病原体和环境侵袭的第一道防线。皮肤还具有重要的体内平衡功能，如减少水分流失和有助于调节体温。皮肤的结构及其细胞组成协同工作，以防止感染并应对来自外界的物理和化学挑战。在这篇综述中，我们讨论了角质形成细胞、成纤维细胞和脂肪细胞等结构细胞如何有助于屏障免疫。我们还讨论了常驻于稳态皮肤中的特化免疫细胞，包括朗格汉斯细胞、真皮巨噬细胞和真皮树突状细胞以及驻留记忆 T 细胞等单核吞噬细胞。衰老会导致癌症和皮肤感染的发病率增加。随着年龄的增长，皮肤结构发生变化，表皮和真皮变薄，水分流失增加，胶原蛋白和弹性蛋白碎片化。此外，皮肤免疫组成发生改变，朗格汉斯细胞减少，抗原特异性免疫降低，调节性群体如 Foxp3 调节性 T 细胞增加。这些改变共同导致老年人的屏障免疫下降，部分解释了他们对癌症和感染的易感性增加。
