Immunological host defense of the skin.

The experimental data presented and reviewed in this manuscript speak in favor of the existence of a skin-specific immune surveillance system for which Streilein [3] has coined the term SALT (skin-associated lymphoid tissues). SALT is comprised of (a) potent antigen presenting cells (LC); (b) distinctive populations of T lymphocytes some of which preferentially infiltrate the epidermis; (c) keratinocytes which produce several immunomodulatory cytokines, and (d) a set of draining peripheral lymph nodes that contain, along with the dermis, blood vessels with endothelial cells whose surface capture lymphocytes passing through the blood. An increasingly better understanding of the circuits and signals of SALT will hopefully result in the development of strategies to prevent a breakdown of this important host-defense mechanism.