Repeated low-dose ultraviolet (UV) B exposures of humans induce limited photoprotection against the immune effects of erythemal UVB radiation.
BACKGROUND
Exposure of human subjects to ultraviolet (UV) B radiation causes immunosuppression. Most experiments to date have not tested the effects of low daily doses of UVB radiation.


OBJECTIVE
To ascertain whether photoprotection against several UV-induced immune effects might develop following repeated exposure.


METHODS
Groups of approximately 30 healthy individuals were given whole-body UVB irradiation on each of 10 consecutive days with 0.7 minimal erythema dose, or whole-body irradiation as before followed by a single erythemal UVB dose on a small body area, or irradiated only with a single erythemal UVB dose on a small body area, or were not irradiated. They were sensitized with diphenylcyclopropenone (DPCP) 24 h after the final dose, and skin biopsies collected to assess cytokine mRNA expression and the number of cells with thymine dimers and expression cyclooxygenase (COX)-1 and COX-2.


RESULTS
The contact hypersensitivity (CHS) response to DPCP was significantly lower in the three irradiated groups compared with the unirradiated controls, while cutaneous interleukin (IL)-1beta, IL-6, IL-10 and tumour necrosis factor-alpha mRNAs, COX-1 and COX-2 and thymine dimers were all significantly higher. When the single erythemal UVB dose was given following the repeated low exposures, a slight downregulation in cytokine expression and thymine dimer formation was indicated.


CONCLUSIONS
The repeated low doses of UVB protected to a limited extent against the effects of an erythemal UVB dose on cytokine expression and thymine dimer formation, but not on CHS or COX enzymes.
Narbutt
J
J
Department of Dermatology, Medical University of Lodz, Krzemieniecka 5, 94-017 Lodz, Poland. joanna.narbutt@onet.pl
Lesiak
A
A
Sysa-Jedrzejowska
A
A
Wozniacka
A
A
Cierniewska-Cieslak
A
A
Boncela
J
J
Jochymski
C
C
Kozlowski
W
W
Zalewska
A
A
Skibinska
M
M
Norval
M
M
D000293:Adolescent; D000328:Adult; D051545:Cyclooxygenase 1 / Q000378:metabolism; D051546:Cyclooxygenase 2 / Q000378:metabolism; D016207:Cytokines / Q000096:biosynthesis / Q000235:genetics; D004249:DNA Damage; D003877:Dermatitis, Contact / Q000209:etiology / Q000276:immunology / Q000517:prevention & control; D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D004890:Erythema / Q000209:etiology / Q000276:immunology* / Q000517:prevention & control; D005260:Female; D006801:Humans; D007108:Immune Tolerance / Q000187:drug effects*; D008297:Male; D011740:Pyrimidine Dimers / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D011832:Radiation Injuries / Q000209:etiology / Q000276:immunology* / Q000517:prevention & control; D011835:Radiation Protection / Q000379:methods*; D012867:Skin / Q000378:metabolism / Q000528:radiation effects; D012880:Skin Pigmentation / Q000528:radiation effects; D014466:Ultraviolet Rays; D015854:Up-Regulation / Q000528:radiation effects
D016207:Cytokines; D011740:Pyrimidine Dimers; D012333:RNA, Messenger; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2