Modulation of immune function by UV radiation.

In addition to its carcinogenic activity, ultraviolet (UV) radiation is capable of modifying certain immunologic reactions. Immunologic alterations induced in mice by UV radiation include both local and distant effects. Local alterations result from a direct effect of UV radiation on an immune reaction that takes place at the site of irradiation. Distant alterations are those in which exposure of skin to UV radiation at one site modifies an immune reaction occurring at a distant, unexposed site. Based on recent studies, we propose that there may be two types of distant alterations. One is nonspecific, may be due to accumulation of leukocytes at the site of UV-induced inflammation, and is exemplified by the suppression of delayed hypersensitivity and local graft-versus-host (GVH) reactions. The second may result from DNA damage, may involve a soluble mediator, and is manifested by the systemic suppression of contact hypersensitivity and the formation of antigen-specific suppressor T lymphocytes. These immunologic effects of exposure to UV radiation may be important in the pathogenesis of skin cancer and other cutaneous diseases.