Keratinization, Barrier Development and Skin Immune System

초록

Title: Keratinization, Barrier development and Skin Immune System 1. Keratinization and barrier development - The skin is covered by the epidermis, a cornified, stratified epithelial cellular sheet that is equipped with a barrier formed by the stratum corneum and tight junctions. Figure 1. Basic structure of the epidermis and major epidermal barriers. - The stratum corneum is an air?liquid interface barrier on the body surface that prevents excessive water loss (inside?outside barrier) and the entry of harmful substances from the environment (outside?inside barrier). - The stratum corneum barrier is composed of corneocytes and intercorneocyte water- impermeable lipid lamellae. Corneocytes are wrapped with cornified cell envelope and corneocyte lipid envelope and contain keratin filaments associated with filaggrin, which is degraded to natural moisturizing factors. Figure 2. Multidomain structure of the stratum corneum and multistep maturation and degradation of filaggrin - The tight junctions seal the intercellular space between neighboring cells at the second layer in the stratum granulosum and form a liquid?liquid interface barrier that limits molecular movement through the paracellular pathway. Figure 3. Tight junction (TJ) barrier in simple and stratified epithelial cellular sheets. - Langerhans cells are located in the epidermis under the tight junction barrier in steady state but extend their dendrites to the outside tight junction barrier upon activation to capture external antigens at the tips of the dendrites. - Antimicrobial peptides, lipids, the acidic pH of the stratum corneum, and continuous daily desquamation (daily detachment of dead skin cells) control the skin microbiota and protect us from infection by bacteria, yeasts, fungi, and viruses. 2. Skin immune system - The skin immune system has an innate and an adaptive component. - Innate immune system has multiple different cellular subsets that have in common rapid re