Immunology of the Skin

The skin is a complex organ that not only acts as a barrier against infection and environmental insults but also uses the immune system for protection. There are two categories of skin immune defense: innate (or nonadaptive) immune responses and adaptive immune responses. The innate immune response is the first line of defense against pathogens. Adaptive immunity is a second-line defense response that occurs as a protection mechanism from microbial antigens. Humoral immunity is the type of adaptive immunity that is mediated by antibodies produced by plasma cells. Cell-mediated immunity is mediated by T lymphocytes. Various types of immune cells are found within the skin, forming a complex network called the “skin immune system.” In addition, all four types of hypersensitivity reactions can involve the skin: type I (immediate type), type II (cytotoxic type), type III (immune complex-mediated), and type IV (delayed type).