Waveband and Dose Dependency of Sunlight‐induced Immunomodulation and Cellular Changes^†

Abstract

Both the UVB and UVA wavebands within sunlight are immunosuppressive. This article reviews the relationship between wavebands and dose in UV-induced immunosuppression mainly concentrating on responses in humans. It also contrasts the effects of UVB and UVA on cellular changes involved in immunosuppression. Over physiological sunlight doses to which humans can be exposed during routine daily living or recreational pursuits, both UVA and UVB suppress immunity. While there is a linear dose relationship with UVB commencing at doses less than half of what is required to cause sunburn, UVA has a bellshaped dose response over the range to which humans can be realistically exposed. At doses too low for either waveband to be suppressive, interactions between UVA and UVB augment each other, enabling immunosuppression to occur. At doses beyond where UVA is immunosuppressive, it still contributes to sunlightinduced immunosuppression via this interaction with UVB. While there is little research comparing the mechanisms by which UVB, UVA and their interactions can cause immunosuppression, it is likely that different chromophores and early molecular events are involved. There is evidence that both wavebands disrupt antigen presentation and effect T cell responses. Different individuals are likely to have different immunomodulatory responses to sunlight.

Ultraviolet A within Sunlight Induces Mutations in the Epidermal Basal Layer of Engineered Human Skin

“…The dose of ssUV used (1.4 J/cm 2 ) would be delivered by 36 minutes exposure to sunlight in early spring in Sydney, Australia, at midday (0.64 mW cm 2 ). 33 Clearly, at more extreme times of year, such as mid summer or winter, shorter or longer exposure times would be required. Therefore, this dose is relatively low and achievable by natural sun exposure.…”

Oxidative Stress and Skin Cancer: An Overview

“…Studies have shown that UVB radiation produces a variety of adverse effects that includes DNA damage [14,15], mutations in key regulatory genes [16], inflammation [17,18], immuno-suppression [19,20], photo-aging and skin cancer [21,22]. UVB is directly absorbed by cellular DNA leading to the formation of DNA lesions primarily cyclobutane pyrimidine dimers and pyrimidine (6-4)-pyrimidone photoproducts [13,23].…”

Systemic Low-Dose UVB Inhibits CD8 T Cells and Skin Inflammation by Alternative and Novel Mechanisms

“…Some of the hallmarks of this immunosuppression include UVB-induced genetic mutations in skin cells, circulation of cis-UCA from the isomerization of trans-UCA, production of reactive oxygen species (ROS), and generation of regulatory T and B cells that can transfer suppression into UVB-naïve mice. 3 Because UVB has both detrimental and beneficial effects on the immune system, it is critical to understand the mechanisms regulated by UVB so that effective prophylactic and palliative therapies can be designed for skin diseases, such as skin cancer, and immune-mediated diseases in internal organs, such as multiple sclerosis.…”