Ultraviolet A1 (340-400 nm) irradiation and systemic lupus erythematosus.

Short wavelengths of ultraviolet (UV) light are clearly harmful in systemic lupus erythematosus (SLE), but the action of long UV wavelengths in SLE is more enigmatic. In a series of animal and human studies, long-wavelength UV radiation, i.e., radiation in the ultraviolet-A1 (UVA1) range (340-400 nm), has proven effective in the treatment of SLE. Disease amelioration and a marked decrease in mortality followed ultraviolet-A (UVA) radiation (320-400 nm) of the New Zealand White/New Zealand Black mouse model of lupus. A follow-up study in the same animal suggested that the longer wavelengths (UVA1, 340-400 nm) in the UVA wave band were primarily responsible. There followed four human studies. The first three of these provided data indicating that low-dose UVA1 radiation significantly reduced constitutional symptoms, joint pain, rashes, and the systemic lupus activity measures, a validated gauge of disease activity in SLE. The fourth human study showed that the therapeutic action of low-dose UVA1 action persisted or progressed long term, a period averaging 3.4 y. UVA1 effects on DNA repair, cell-mediated immunosuppression, tumor necrosis factor alpha release, and apoptosis contrast markedly with those of ultraviolet B (UVB, 280-320 nm) radiation and afford a possible basis for the salutary action of this modality of treatment. The unique features of UVA1 wavelengths may be suited to further therapeutic use, not only in SLE but also in other immunologic disorders.