Objective: To investigate whether repeated exposures to low-dose UV or solar-simulated radiation induce apoptosis of peripheral blood mononuclear cells.
Design: Cohort study in a healthy population.
Setting: Departments of Dermatology and Hematology, Medical University of Lodz, Lodz, Poland.
Participants: Ninety-eight healthy volunteers were divided into the following 4 groups: group A, whole-body irradiated with a 0.7-minimal erythema dose (MED) of UV-B daily on 10 consecutive days followed by a single dose of 3 MEDs on a small body area 24 hours later; group B, whole body irradiated with 120 J/m(2) solar-simulated radiation (10 consecutive days, then single-dose UV-B exposure of 3 MEDs on a small body area after 24 hours); group C, irradiated with a single UV-B dose of 3 MEDs on a small body area; and group D, irradiated with a single UV-B dose of 4 MEDs on a small body area.
Main outcome measure: Apoptosis of peripheral blood mononuclear cells as well as expression of several apoptosis-regulating proteins in response to irradiation.
Results: Ten daily whole-body suberythemal exposures to UV-B or solar-simulated radiation enhanced the apoptosis of peripheral blood mononuclear cells, while the single erythemal doses on the small body area, either on their own or following the repeated exposures, did not increase the level significantly. Increase in Bax and p73 protein expression and down-regulation of Mcl-1 and Bcl-2 correlated with enhanced apoptosis.
Conclusion: Repeated suberythemal UV exposures enhance the apoptosis of peripheral blood mononuclear cells in healthy subjects.