Abstract
Photoimmunology deals primarily with the effect of the ultraviolet (UV) light on the skin's immune system. This chapter introduces the skin's immune system and discusses the effects of light. The skin and its draining lymph nodes cooperate to provide an effective immune surveillance system. The epidermis is the source of sensitizing as well as tolerizing signals. Based on immuno phenotyping with monoclonal antibodies, they appear to be of bone marrow origin and a unique member of the family of la antigen-hearing cells necessary for the initiation of T cell-dependent immune responses. The expression of tissue-specific homing receptors is accompanied by an expression of corresponding adressins on vasculo-endothelial cells. This promotes the migration of memory T cells into the dermis. After renewed stimulation by antigen-presenting cells, T cells can undergo cloned expansion. The result is the generation of effector cells and molecules that eliminate the pathogen or aggressor agent. Humans may vary in their susceptibility to the UV-induced inhibition of contact hypersensitivity. Human epidermal cells obtained after exposure to UVB radiation are capable of activating suppressor–inducer lymphocytes.
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