Immunopathology of Skin Ailments

Skin is the body’s largest organ. The primary function is to act as a shield that protects internal organs from physical and chemical attacks, pathogen invasion and excessive loss of water. The body is rich in immune cells, forming a complex network called as the “skin immune system”, as the main immunological barrier to the external environment. Any immune system disruption or defects can lead to immunological skin diseases. Excessive and undesirable immune responses can cause hypersensitivity or autoimmune diseases, while hypoimmunity can lead to infectious diseases and skin tumor. In body, the immune system is located in both major structural compartments: epidermis and dermis, and consists of several essential types of immunocompetent cells. Primary skin-resident immune cells, Langerhans cells (LCs) and melanocytes that produce melanin inhabit epidermis, while other types of immune-specialized cells, such as various subpopulations of dendritic cells (DCs), macrophages, and several types of T cells reside in the deeper layer — dermis. The efficacy of the skin immune system strongly depends on the close interplay and interaction between immune cells and the skin environment, such as adjacent keratinocytes and fibroblasts. The fundamental premise for protective immunity is the ability to distinguish between self and non-self. This ability is acquired during the growth of the fetus. In the normal system, when the above process fails, immune-mediated disease occurs. Some of the most interesting and challenging issues in immune-mediated dermatological diseases are discussed in this book chapter.