Time–course study of different innate immune mediators produced by UV‐irradiated skin: comparative effects of short and daily versus a single harmful UV exposure

Abstract

SummaryThe modulatory effects of solar UV radiation on the immune system have been widely studied. As the skin is the main target of UV radiation, our purpose was to compare the impact on skin innate immunity of two contrasting ways to be exposed to sunlight. Hairless mice were UV irradiated with a single high UV dose simulating a harmful exposure, or with repetitive low UV doses simulating short occasional daily exposures. Skin samples were taken at different times after UV irradiation to evaluate skin histology, inflammatory cell recruitment, epidermal T-cell population and the mitochondrial function of epidermal cells. The transcriptional profiles of pro-inflammatory cytokines, chemokines, antimicrobial peptides and Toll-like receptors were evaluated by RT-PCR and ELISA in tissue homogenates. Finally, a lymphangiography was performed to assess modification in the lymphatic vessel system. A single high UV dose produces a deep inflammatory state characterized by the production of pro-inflammatory cytokines and chemokines that, in turn, induces the recruitment of neutrophils and macrophages into the irradiated area. On the other hand, repetitive low UV doses drive the skin to a photo-induced alert state in which there is no sign of inflammation, but the epithelium undergoes changes in thickness, the lymphatic circulation increases, and the transcription of antimicrobial peptides is induced.

Daily very low UV dose exposure enhances adaptive immunity, compared with a single high‐dose exposure. Consequences for the control of a skin infection

“…As previously reported, UVr is able to perturb the skin barrier function , . Moreover, as shown here, UVr can also modulate the adaptive immune system, depending on the dose of radiation received.…”

“…Skin exposure to an shUVd and rlUVd produces changes in the innate immune system as we have previously reported . Based on those results, we have decided to evaluate the possible effects of UVr on adaptive immunity.…”

Narrowband UVB Phototherapy for Clinically Isolated Syndrome: A Trial to Deliver the Benefits of Vitamin D and Other UVB-Induced Molecules

“…These peptides have modest antimicrobial activity but rather pleiotropic immunoregulatory properties (52). They are produced in sub-erythemal UV-irradiated skin in the absence of any inflammation (53); they include cathelicidin LL-37 and the α- and β-defensins (52). As shown in a murine model, β-defensins via induction of T-regulatory cells can prevent and mitigate EAE (54).…”

DNA damage in protective and adverse inflammatory responses: Friend of foe?

“…A recent study closely monitored molecular events instigated in the skin upon single high dose "harmful" UV exposure and upon multiple low dose "daily" exposure [71]. It was found that acute inflammation was only triggered by a single high UV dose; the response to chronic low UV doses was distinct and didn't implicate strong inflammatory signals.…”