Suppression of experimental autoimmune encephalomyelitis by 300-315Â nm ultraviolet light

Multiple sclerosis (MS) is a chronic debilitating disease, with lowest incidence in equatorial regions and highest incidence in temperate regions. This relationship is believed to be related to sunlight or UV light exposure. Recent evidence with experimental autoimmune encephalomyelitis (EAE), an animal model of MS, established that this suppression is not mediated by vitamin D production. UV is comprised of three general wave bands: UVC (100-280 nm), UVB (280-320 nm) and UVA (320-400 nm). In the present study we used four lamps that emit different wavelengths of UV: (1) broad band UVB (BB-UVB: 280-320 nm); (2) narrow band UVB (NB-UVB: 300-315 nm); (3) broad band UVA (BB-UVA: 300-400 nm); and (4) long wavelength UVA (UVA-1: 340-400 nm). The effect of these light sources was studied in vitamin D-sufficient C57BL/6 mice. The NB-UVB largely accounted for the suppression and delay of onset of EAE by BB-UVB. In contrast, UVA-1 failed to suppress EAE severity at low (∼2.5 KJ/m2), medium (∼5.0 KJ/m2) and high (∼10.0 KJ/m2) doses. Serum calcium and 25-(OH)D3 levels were unchanged after both NB-UVB and UVA-1 treatments. The results demonstrate that NB-UVB (300-315 nm) is largely responsible for light-induced suppression of EAE and its effect is not via production of vitamin D.