Photoimmunology: how ultraviolet radiation affects the immune system

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Ultraviolet (UV) radiation is a ubiquitous component of the environment that has important effects on a wide range of cell functions. Short-wavelength UVB radiation induces sunburn and is a potent immunomodulator, yet longer-wavelength, lower-energy UVA radiation also has effects on mammalian immunity. This Review discusses current knowledge regarding the mechanisms by which UV radiation can modify innate and adaptive immune responses and how this immunomodulatory capacity can be both beneficial in the case of inflammatory and autoimmune diseases, and detrimental in the case of skin cancer and the response to several infectious agents.

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Fig. 1: UVR absorption by chromophores and damage recognition.
Fig. 2: Mechanisms of UVR-induced immunomodulation.
Fig. 3: The innate immune response is stimulated by the release of damage-associated molecular patterns following exposure to UVR.


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The authors acknowledge research support by grants from Michigan State University Gran Fondo funds, NIH R00 CA177868, the German Federal Ministry for Education and Research (BMBF: 02NUK036C/KAUVIR), NIH R01AI052453 and NIH R01AR069653. The authors thank W. Shoemaker (Michigan State University), T. Haarmann-Stemmann (IUF) and C. Esser (IUF) for their help with manuscript preparation.

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Correspondence to Jamie J. Bernard.

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Contact hypersensitivity

(CHS). A T cell-mediated and antigen-specific inflammatory response in which the exposure of epidermal cells to exogenous haptens results in a delayed-type hypersensitivity reaction that can be experimentally measured and quantified.


The parts of a photoreceptor that absorb photons of light, using a mechanism that involves a change in configuration.


The production of melanin pigments by melanocytes in the basal layer of the epidermis.


A group of heterocyclic macrocycle organic compounds composed of four modified pyrrole subunits interconnected at their α-carbon atoms by methine bridges.

Singlet oxygen

The reactive oxygen species 1O2.

Urocanic acid

(UCA). A breakdown (deamination) product of histidine that is an important epidermal chromophore for ultraviolet radiation.

Nucleotide excision repair

(NER). A mechanism to remove DNA damage, such as the thymine dimers and 6,4-photoproducts that are induced by ultraviolet radiation.

Xeroderma pigmentosum

An autosomal recessive genetic disorder that causes cellular hypersensitivity to ultraviolet radiation as a result of a defect in the DNA repair system.

Reactive oxygen intermediates

(ROIs). Successive one-electron reduction products of O2, including superoxide anions, hydrogen peroxide and hydroxyl radicals; ROIs are chemically reactive with unpaired electrons.

Minimal erythemal dose

The threshold dose of ultraviolet radiation that can produce sunburn.


An uncommon inflammatory myopathy characterized by degenerative changes to the muscles and skin.


1-Chloro-2,4-dinitrobenzene is an organic, potent contact allergen.

Psoralen plus UVA

A therapy for skin conditions, including psoriasis, eczema and vitiligo, that is composed of a plant-derived ultraviolet (UV)-sensitizer compound (psoralen), combined with UVA radiation (long wavelength radiation).


A common and highly contagious skin infection that mainly affects infants and children; it usually occurs as red sores on the face.

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