LETTER
Reply to Handunnetthi and Ramagopalan: UV radiation, experimental autoimmune encephalomyelitis, and multiple sclerosis Handunnetthi and Ramagopalan have questioned the validity of the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS) (1), the model we have used in our studies relating to MS (2). As with any animal model of human disease, the EAE model has its limitations. For example, in the mice, the disease is induced through immunization, as opposed to occurring spontaneously, as is the case with MS. Despite these problems, the EAE model has been instrumental in MS research. The EAE model has provided insight into the underlying mechanisms of MS pathology. Preclinical work in the EAE model has directly led to the development of three different treatment modalities for MS, including glatiramer acetate, mitoxantrone, and natalizumab (3). The EAE model also allows researchers the manipulation of mice genetically that simply is not possible with human subjects. Therefore, although studies in the EAE model cannot be “unequivocally extrapolated” to answer questions relating to MS, they certainly provide a starting point for the exploration of whether UV radiation, vitamin D, or both are involved in determining MS susceptibility. When studying the effect of UV radiation itself, the problem is that UV radiation also produces vitamin D. We analyzed the effect of UV on circulating 25-OH-D3 levels and the effect of 25-OH-D3 levels on EAE independent of UV radiation. Clearly, the level of 25-OH-D3 required to suppress EAE was much greater than the level reached by our UV treatment. In our experiments “suppression” means that the treatment group showed a significant decrease in the average clinical scores compared with its control group. We used two different diets in the studies we reported. In our hands, mice fed a chow diet consistently had higher EAE scores than mice fed a purified diet.
www.pnas.org/cgi/doi/10.1073/pnas.1008059107
Thus, the untreated control animals on the chow diet had a higher score than the controls on the purified diet. 1,25-(OH)2D3 is effective only when delivered at doses that cause hypercalcemia (4). In addition, hypercalcemia independent of vitamin D can suppress EAE (5). Thus, calcium plays a critical role in the protective mechanisms underlying 1,25-(OH)2D3 treatment. In contrast, treatment with UV radiation had no effect on serum calcium levels. This observation, coupled with the fact that UV radiation does not cause hypercalcemia in human populations exposed to large amounts of sunlight, argues against vitamin D being the sole cause of protection against MS. However, it is possible that localized production of 1,25-(OH)2D3 may be important for protection. To address this issue we are currently carrying out experiments in mice lacking the 1α-hydroxylase and/or vitamin D receptor gene. Although we agree that the most conclusive evidence elucidating the role of vitamin D and UV will come from clinical trials, we caution against disregarding evidence simply because it was derived from studies using the EAE model. As stated by Steinman and Zamvil, “To study a disease such as MS, without support from available animal models, is to unnecessarily create obstacles in a task that is complicated enough” (3). Bryan R. Becklund, Kyle S. Severson, Souriya V. Vang, and Hector F. DeLuca1 Department of Biochemistry, University of Wisconsin–Madison, Madison, WI 53706 1. Handunnetthi L, Ramagopalan SV (2010) UV radiation, vitamin D, and multiple sclerosis. Proc Natl Acad Sci USA 107:E130. 2. Becklund BR, Severson KS, Vang SV, DeLuca HF (2010) UV radiation suppresses experimental autoimmune encephalomyelitis independent of vitamin D production. Proc Natl Acad Sci USA 107:6418–6423. 3. Steinman L, Zamvil SS (2006) How to successfully apply animal studies in experimental allergic encephalomyelitis to research on multiple sclerosis. Ann Neurol 60:12–21. 4. Cantorna MT, Humpal-Winter J, DeLuca HF (1999) Dietary calcium is a major factor in 1,25-dihydroxycholecalciferol suppression of experimental autoimmune encephalomyelitis in mice. J Nutr 129:1966–1971. 5. Meehan TF, Vanhooke J, Prahl J, Deluca HF (2005) Hypercalcemia produced by parathyroid hormone suppresses experimental autoimmune encephalomyelitis in female but not male mice. Arch Biochem Biophys 442:214–221.
Author contributions: B.R.B. and H.F.D. designed research; B.R.B., K.S.S., and S.V.V. performed research; B.R.B., S.V.V., and H.F.D. analyzed data; and B.R.B. and H.F.D. wrote the paper. The authors declare no conflict of interest. 1
To whom correspondence should be addressed. E-mail:
[email protected].
PNAS | August 17, 2010 | vol. 107 | no. 33 | E131
