Therapeutic photoimmunology: photoimmunological mechanisms in photo(chemo)therapy.

Ultraviolet radiation, either alone or in combination with photosensitizing agents, is widely used for the treatment of skin diseases. The efficacy of photo- and photochemotherapeutic modalities is thought to result, at least in part, from the induction of immunomodulatory effects. In particular, UV radiation has been shown to affect (i) the production of soluble mediators, (ii) the expression of cell-surface receptors and (iii) to induce apoptosis in pathogenetically relevant cells. UVB radiation-induced immunomodulatory effects are limited to the epidermis, whereas UVA radiation affects both epidermal and dermal cell populations. UVB and UVA radiation can exert essentially identical immunomodulatory effects, which result, however, from different photobiological mechanisms.