ABSTRACT
The immune system is called upon to provide protection against an enormously diverse array of environmental and endogenous pathogens. For an even longer period of time, immunologists and dermatologists have realized that the relationship between the immune system and the skin is unique. This notion was formalized in 1978 into the concept of Skin-Associated Lymphoid Tissues (SALT). In an early formulation of SALT it was hypothesized that there is a specialization of dermal microvessels that promote the immigration of skin-seeking lymphocytes from the blood. Although most leukocytes from the blood can and do gain access into the skin via the dermal vascular bed, special attention has been paid to the migration of T lymphocytes since the cells are considered to be absolutely critical to cutaneous immunity. The dermis serves as a reservoir for the replenishment and perhaps the terminal differentiation of epidermal Langerhans cells.
