Differential effect of phototherapy on the activities of human natural killer cells and cytotoxic T cells

Exposure to ultraviolet B (UV-B) light is recognized to induce suppression of certain immune responses, particularly delayed hypersensitivity. However , its effect on cytotoxic T lymphocyte (CTL) activity, of major importance in the resistance to viruses and tumours, has not been assessed to the same extent. In this study five normal subjects, seropositive for herpes simple x virus (HSV), underwent a standard course of broadband UV-B therapy, as us ed in the treatment of psoriasis. They received whole-body irradiation thri ce weekly for four weeks with incremental doses dependent on skin type. Blo od samples were taken immediately before, at two time points during, and at the end of the therapy. An HSV-specific CTL assay was performed using auto logous B cells transformed with Epstein-Barr virus as targets. No consisten t modulation in CTL activity was obtained as a result of the therapy. The C TLs were separated into CD4 and CD8 subsets by positive selection and, agai n, no effect of irradiation on CTL activity within each of these two popula tions was observed. In contrast, the natural killer (NK) cell activity, ass essed by the lysis of K562 cells, was significantly reduced at the first ti me point after the initiation of the phototherapy in all five subjects, and it continued to decline as the treatment progressed. Thus a differential e ffect of UV-B exposure on cytotoxic activity has been demonstrated: the HSV -specific CTL response is unchanged, while the NK response is suppressed. ( C) 1998 Elsevier Science S.A. All rights reserved.