Phototherapy utilizes the beneficial effects of ultraviolet (UV) wavelengths to affect immunoregulatory functions. UV light phototherapy using narrowband UV-B (NB-UVB) and bath-psoralen UV-A (bath-PUVA) therapy are well-established treatments for psoriasis. Dual-action mechanisms of UV phototherapy have been identified: apoptosis and immune suppression. NB-UVB depletes pathogenic T cells by inducing apoptosis and regulatory T cells. Other wavelengths are also utilized for phototherapy, namely 308-nm excimer light and 312-nm flat-typed NB-UVB. Excimer light (308-nm) therapy effectively targets the affected skin without unduly exposing other areas and increases the levels of regulatory T cells. Phototherapy improves impaired resting regulatory T cells and increases activated regulatory T cells in patients with psoriasis. Intensive studies of phototherapy effects have led to several improvements in the design, protocols, and light sources, such as UV light-emitting diodes, thereby providing several options for patients with refractory skin disease, such as psoriasis.
Keywords: apoptosis; excimer light; immune suppression; narrowband ultraviolet B; regulatory T cells.
© 2018 Japanese Dermatological Association.