EVIDENCE THAT SINGLET OXYGEN-INDUCED HUMAN T-HELPER CELL APOPTOSIS ISTHE BASIC MECHANISM OF ULTRAVIOLET-A RADIATION PHOTOTHERAPY

Ultraviolet A (UVA) irradiation is effectively used to treat patients with atopic dermatitis and other T cell mediated, inflammatory skin di seases. In the present study, successful phototherapy atopic dermatiti s was found to result from WA radiation-induced apoptosis in skin-infi ltrating T helper cells, leading to T cell depletion from eczematous s kin. In vitro, UVA radiation-induced human T helper cell apoptosis was mediated through the FAS/FAS-ligand system, which was activated in ir radiated T cells as a consequence of singlet oxygen generation. These studies demonstrate that singlet oxygen is a potent trigger for the in duction of human T cell apoptosis. They also identify singlet oxygen g eneration as a fundamental mechanism of action operative in photothera py.