Skin as an Immunocompetent Organ in Health and Disease

Abstract

Covering the human body, the skin represents the main interface organ directly in contact with the environment. The skin divides wet and dry, warm and cold, own and foreign, thus enabling us to keep all of our body systems in working order. Here, at the very border of our entire organism, the immunologic properties of the skin, our largest organ, are of vital importance. In addition to its well-known physical protective properties, human skin is a target for a series of agents, e.g., of microbiologic or physical nature, and an amazing source of various mediators that either initiate or accompany defense responses, e.g., inflammation (Fig. 1). Impaired barrier function, ultraviolet (UV) radiation, cell death, and encounter with bacteria, viruses, fungi, and protozoa belong to the broad spectrum of signals that are capable of initiating this inflammatory response, thus activating the cutaneous immune system. The aim of this chapter is not to go into experimental details, which maybe read in excellent reviews on this topic [1, 2], but rather to provide the reader with an overview of simple and basic concepts that have been developed in almost two decades of progress in immunodermatologic research for a better understanding of the rationale of the strategies discussed in this book.