Haftek M
U. 346 INSERM affiliée au CNRS, Peau Humaine et Immunité , Hôpital E.-Herriot, 69437 Lyon.
Ann Dermatol Venereol. 2002 Jan;129(1 Pt 2):117-22.
Epidermal differentiation is a continuous process, constituting and renewing a protective layer at the skin surface: the stratum corneum, composed of cornified keratinocytes that is a barrier to water diffusion. Massive loss of physiologic liquids is one of the severest consequences of extensive burns. The stratum corneum also protects the subjacent tissues from xenobiotic aggression, ultraviolet radiation (70 p. cent of UVB absorption) and from mechanic aggression. The integrity of the stratum corneum depends on three elements: 1) the physico-chemical quality of the cornified cells, 2) the persistence of mechanical junctions uniting these cells and 3) the organization and composition of the lipid "mortar" in the intercellular spaces. Since all these components are issued from the keratinocyte differentiation process, any perturbation may, in time, induce modifications in the "barrier" function of the epidermis. The barrier quality varies, depending on its localization (soles of the feet, palms of the hands and transitional epidermis of the lips), during skin healing (priority to keratinocyte proliferation to the detriment of maturation) under the influence of treatment (retinoids, vitamin D derivatives), in the course of aging and diseases: ichtyosis and other keratinization genodermatoses, benign (including psoriasis) and malignant hyperproliferative diseases. Furthermore, the relative impermeability of the stratum corneum is an important factor limiting the penetration and diffusion of allergens, but also local drugs delivered with local and systemic trans-epidermal treatments. Further knowledge is required on the function of the epidermal barrier and the mechanism regulating cohesion/desquamation of the stratum corneum to understand certain hereditary diseases, improve efficacy of topical therapeutic products and optimize cosmetic formulations.
表皮分化是一个持续的过程，在皮肤表面形成并更新一层保护层：角质层，由角化的角质形成细胞组成，是水分扩散的屏障。生理液体的大量流失是大面积烧伤最严重的后果之一。角质层还可保护下方组织免受外源性侵害、紫外线辐射（吸收70%的中波紫外线）以及机械性侵害。角质层的完整性取决于三个因素：1）角化细胞的物理化学性质；2）连接这些细胞的机械连接的持久性；3）细胞间空间中脂质“灰浆”的组织和组成。由于所有这些成分都源自角质形成细胞的分化过程，任何干扰最终都可能导致表皮“屏障”功能的改变。屏障质量会因部位（脚底、手掌和唇部的过渡表皮）、皮肤愈合过程（角质形成细胞增殖优先而成熟受损）、治疗（维甲酸、维生素D衍生物）的影响、衰老过程以及疾病（鱼鳞病和其他角化性遗传性皮肤病、良性（包括银屑病）和恶性增殖性疾病）而有所不同。此外，角质层的相对不渗透性是限制变应原渗透和扩散以及局部和全身经皮治疗所用局部药物渗透和扩散的重要因素。需要进一步了解表皮屏障的功能以及调节角质层黏附/脱屑的机制，以理解某些遗传性疾病、提高局部治疗产品的疗效并优化化妆品配方。
