PHOTODERMATOLOGY: CURRENT PRINCIPLES AND PRACTICE
Ultraviolet A Radiation: Its Role in Immunosuppression and Carcinogenesis
Dec
2011
Vol. 30. No. 4
Ultraviolet A (UVA) radiation is immunosuppressive and mutagenic in humans and carcinogenic
in animals. UVA suppresses immunity with a bell-shaped dose response. At doses
equivalent to 15-20 minutes of sun exposure at noon, UVA contributes to approximately
75% of sunlight-induced immunosuppression. A recent action spectrum, indicating that
360-380 nm but not 320-350 nm UVA suppresses immunity in humans, suggests an
important role for reactive oxygen species. UVA also causes an energy crisis in cells, and
normalization of adenosine triphosphate with nicotinamide prevents UVA immunosuppression.
UVA activation of the alternative complement pathway and defects in memory T-cell
development are also involved. Human skin cancers contain mutations in the p53 and BRM
genes that are consistent with being induced by UVA. UVA is also mutagenic in human skin
equivalents. The basal layer of human skin is more susceptible to UVA-induced mutations
than the upper layers. Because skin cancers arise from these basal proliferating cells, this
finding is likely to be important and could be attributable to low levels of the DNA repair
enzyme OGG1 in basal cells. UVA is therefore likely to make a larger contribution to
UVA-induced skin carcinogenesis in humans than is predicted by small animal models as
the result of being immunosuppressive and mutagenic for basal keratinocytes.
Semin Cutan Med Surg 30:214-221 © 2011 Elsevier Inc. All rights reserved.
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