DEVELOPMENT OF AN INVITRO SYSTEM FOR THE ANALYSIS OF ULTRAVIOLET RADIATION-INDUCED SUPPRESSION OF NATURAL-KILLER-CELL ACTIVITY

Previous studies have shown that natural killer (NK) cell activity was suppressed in volunteer subjects exposed to ultraviolet radiation (UVR) from solarium lamps. The present studies were carried out to determine the spectrum of UVR responsible for suppression of NK activity and to develop in vitro methods to analyze the effectiveness of sunscreen agents in prevention of UVR-mediated suppression of NK activity and other aspects of immune function. UVR from a xenon arc lamp source was used to irradiate peripheral blood lymphocytes (PBL) in wells of tissue culture flasks, and transmission interference filters were used to eliminate UVR of particular wavelengths. The results indicated that UVR from this source inhibited NK activity of PBL in a dose-dependent manner with a 50% inhibitory dose of 5.5 mJ/cm2 when unfiltered and 29.6 mJ/cm2 when diluted through cellulose acetate, which gave a UV spectrum similar to that in solar radiation. Equivalent suppression of NK activity was mediated by UV-A (UVR > 315 nm) at dose levels of 4.2 J/cm2, which was approximately 140 times greater than the amount of UV-B (UVR < 315 nm) needed to suppress NK activity. Similar dose-response curves were seen for inhibition of mitogenic responses to phytohemagglutinin except that the latter appeared less sensitive than NK to inhibition by UV-A. These studies suggest that when the greater proportion of UV-A in solar radiation and its greater penetration into skin is taken into account, UV-A may have equivalent or greater direct immunosuppressive effects than UV-B. The mechanisms of their immunosuppressive effects may, however, differ. The in vitro system described here would appear to provide a simple test system for further analysis of UVR-induced immunosuppression.