UVB-INDUCED SUPPRESSION OF THE MIXED EPIDERMAL-CELL LYMPHOCYTE-REACTION IS CRITICALLY DEPENDENT ON IRRADIANCE

The mixed epidermal cell lymphocyte reaction (MECLR) is a commonly use d method to study the effects of ultraviolet B (UVB) radiation on the skin immune system. In UVB experiments dosimetry is very important. Th e influence of irradiance on the MECLR was studied in vitro using Phil ips FS40 lamps with variable UV intensities. Irradiation of isolated e pidermal cells with high irradiance impaired the alloactivating capaci ty more than irradiation with low irradiance. In vivo, the influence o f long-term UVB exposure on the MECLR was studied by treating normal h ealthy volunteers with suberythemagenic doses of UVB thrice weekly dur ing 4 weeks. The first set of experiments, using low irradiance Sylvan ia UV-21 F75/85 W lamps, resulted in a decrease of MECLR responses of 83.1%. In the second set of experiments performed a year later, employ ing an identical protocol except for the use of high irradiance Waldma nn UV-21 F8S/100 W lamps, an increase of MECLR responses of 99.7% was observed. Volunteers of both sets of experiments received equal doses of UVB. In conclusion, this study shows that in vitro UVB-induced supp ression of the MECLR is critically dependent on irradiance and therefo re might explain contradictory results described in the literature. Th e in vivo data suggest that, comparable to the in vitro experiments, i rradiance may influence the effects of UVB irradiation in vivo. Furthe r experiments should prove whether this is indeed the case.