Editors' ChoiceAutoimmunity

Shedding (UV) Light on Multiple Sclerosis

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Science Translational Medicine  09 Jul 2014:
Vol. 6, Issue 244, pp. 244ec120
DOI: 10.1126/scitranslmed.3009805

Around the globe, the incidence of multiple sclerosis (MS)—a neurological autoimmune disease—is higher in colder latitudes than in warmer ones. In fact, the farther one lives from the equator, the higher the prevalence of MS, prompting speculation about possible roles for sunlight and vitamin D in MS pathogenesis. In a new study, Breuer and colleagues shed new light on the possible mechanism underlying this phenomenon by revealing that ultraviolet (UV) light suppresses neuroinflammation and disease progression in a mouse model of MS and induces an anti-inflammatory response in humans.

MS is characterized by autoimmune activation of inflammatory T cells, which drive inflammation and autoimmune destruction of the protective myelin sheaths that insulate neurons in the brain and spinal cord. Using a common MS mouse model, Breuer and coworkers showed that narrow-band UVB (nbUVB) light treatment significantly suppressed the inflammatory response and prevented demyelination in the spinal cord. The protective effects of nbUVB were dependent on the activation of Langerhans cells in the skin, leading to an increase in the number of tolerogenic (antigen-specific unresponsive) dendritic cells and a marked rise in regulatory T cells (Treg cells), which attenuate overall T cell activation and suppress inflammation. The authors also performed a proof-of-concept clinical study in which 11 MS patients were treated with nbUVB for 6 weeks. Although no clinical changes were observed, increased numbers of tolerogenic dendritic cells and Treg cells were observed only in skin biopsies from treated patients, suggesting that nbUVB might exert similar effects in people as it does in mice.

A precedent for the use of UV light as a therapy for inflammatory diseases already exists: nbUVB is commonly used to treat psoriasis and is easily administered, inexpensive, and well tolerated. However, large clinical studies are now needed to determine whether specific nbUVB regimens have an impact on disease progression in MS patients. In the meantime, this study justifies the need to spend a few more summer days at the beach.

J. Breuer et al., Ultraviolet B light attenuates the systemic immune response in central nervous system autoimmunity. Ann. Neurol. 75, 739–758 (2014). [PubMed]

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