Vitamin D3 Blocks T Helper Cells From Entering the CNS

Vitamin D₃ selectively and reversibly inhibits the migration of T helper cells into the central nervous system (CNS), according to findings from a new study. The authors said the findings could have significant implications for the use of vitamin D as an adjunctive therapy for immune-mediated diseases such as multiple sclerosis (MS).   

The study appeared online December 9 in the Proceedings of the National Academy of Sciences and was authored by Anne R. Gocke, Ph.D., an assistant professor of neurology at the Johns Hopkins University School of Medicine in Baltimore, Maryland, along with colleagues (Grishkan et al., 2013). The authors described their study as "a systematic evaluation of the vitamin D effects on T lymphocytes at each step of their journey to the CNS."

Based mostly on epidemiologic and animal studies, it has been suspected for some time that high-dose vitamin D supplementation might have positive effects on the course of disease in patients with MS. In fact, a clinical study is currently underway at Johns Hopkins looking more closely at that hypothesis.  

Focusing on mechanisms of D₃

In conjunction with the clinical study, Gocke and her group decided to use an animal model to focus on the mechanism of action of vitamin D₃—exactly why supplementation appears to have positive effects.

"By using the animal model of multiple sclerosis, experimental autoimmune encephalomyelitis or EAE, we're trying to determine how these beneficial effects of vitamin D occur, especially the effects of vitamin D on activation and function of T cells," Gocke told MSDF in an interview.

The investigators administered high-dose vitamin D via oral gavage to a group of mice and at the same time inoculated them with myelin oligodendrocyte glycoprotein (MOG), which is associated with development of EAE. A control group of mice received no vitamin D prior to inoculation with MOG.

How would the vitamin D administered to the mice translate to human subjects with MS? Gocke said an equivalent dose in humans might work out to be approximately 10,000 IU per day, which is the dosage being used in the clinical trial at Johns Hopkins.

In the current study, the investigators first tracked the mice over time to see how their disease progressed. As would be expected based on previous studies, the researchers did not see EAE develop in animals that had received vitamin D, Gocke said.

Then the researchers sacrificed the animals at various times and used several techniques—including ELISA, flow cytometry, complete blood counts, and bioluminescent imaging—to track the T cells and determine how and where they were migrating.

T cells barred from CNS

"We found that the T cells were activated in the periphery, but they were not getting into the brain or the spinal cord," Gocke said. The data showed that myelin-reactive T helper cells are successfully generated in the presence of vitamin D₃, that they secrete proinflammatory cytokines, and that they do not preferentially differentiate into suppressor T cells. The T cells were able to migrate from lymph nodes and make their way into the peripheral circulation and subsequently to sites of immunization. 

However, in mice supplemented with vitamin D, T cells were blocked from entering the parenchyma and instead remained in the peripheral circulation.    

"There have been a number of studies showing differentiation of T cells, but our study is the first to show the effects of D₃ on migration and trafficking of immune cells," Gocke said.

Reversible effects are key

Gocke pointed out that some of the newly approved drugs for treating MS, such as natalizumab and fingolimod, like vitamin D₃, work by impairing immune cell trafficking. 

However, one particularly important finding from the present study, Gocke explained, was that, unlike natalizumab and fingolimod, which after cessation can take 6 to 12 weeks to clear the body, vitamin D₃ is cleared very rapidly. "That could prove to be a very good attribute in clinical situations where a patient has a serious infection and their immune function needs to be reestablished," she said.

The authors concluded that their findings provide unique evidence that vitamin D₃ prevents EAE by modulating the migratory phenotype of the pathogenic T helper cells while having no known effect on their priming or effector functions.

MSDF solicited independent comment from Colleen E. Hayes, Ph.D., a biochemist at the University of Wisconsin, Madison. Hayes, like Gocke, has considerable experience studying molecular mechanisms that regulate immune response.

We asked her what she sees as the most important questions yet to be answered regarding the role of vitamin D₃ in managing MS.

She responded (in order of priorities): 

• "Research is needed to determine the optimal amount of supplementary vitamin D₃, and the optimal supplementation schedule (weekly vs. monthly, etc.) to achieve the maximum benefits in those MS patients whose disease will respond to supplementary vitamin D₃."

• "Research is needed to determine which MS patients do not benefit from supplementary vitamin D₃, and what genetic polymorphisms they may be carrying that could be impeding the benefits of vitamin D₃. For example, do the nonresponders have variants of genes involved in vitamin D metabolism that could be shortening the biological half-life of the pro-hormone or hormonal forms of vitamin D, or do they have variants of genes that are downstream of the vitamin D receptor in the several biological pathways, known and unknown, that mediate the beneficial effects of this hormonal system (e.g., IL-10 and IL-10-receptor pathways)? Also, will women show greater responsiveness to supplementary vitamin D₃ than men, and why—could it be sex hormone related?"

• "Research is needed to determine whether MS patients who do not benefit from supplementary vitamin D₃ will benefit from periodic pulse doses of the hormone, 1,25-dihydroxyvitamin D₃, in addition to supplementary vitamin D₃, as an approach to disease management."

• "Research is needed to determine whether supplementary vitamin D₃, given at the first sign of demyelinating disease, will prevent progression to clinically definite MS."

• "Research is needed to determine whether supplementary vitamin D₃, given to biological first-degree relatives of MS patients (particularly sisters and daughters), will reduce the incidence of MS."

• "Research is needed to determine whether supplementary vitamin D₃, given to children, will reduce the incidence of MS and possibly other autoimmune diseases like type 1 diabetes, where low vitamin D status has been implicated as a possible causal factor."

• "Research is needed to determine whether supplementary vitamin D₃, given to adults, will reduce the incidence of other neurodegenerative diseases like Alzheimer’s disease, where low vitamin D status has been implicated as a possible causal factor."

In addition, Hayes pointed out that an important paper, again relating to the topic of immune cell function, was recently published. That study (Hollis and Wagner, 2013), authored by Bruce W. Hollis, Ph.D., of the Medical University of South Carolina in Charleston, along with a coworker, concluded that significant vitamin D needs to be bioavailable on a daily basis to ensure stable circulating concentrations. The implication, they wrote, is that since vitamin D is characterized by a short circulating half-life, variations in dosing could have crucial effects on the outcomes of clinical trials.

Key open questions

• What is the specific molecular signature that allows myelin-reactive T helper cells to breach the central nervous system and invade the parenchyma?

• Why is it that vitamin D appears to have no effect on the generation of pathogenic cells yet prevents those cells from entering the central nervous system?

• What role might vitamin D play in preventing new cases of MS?

• How might the results of this animal-based study translate to clinical management of patients with MS?

Disclosures

Drs. Gocke, Hayes, and Hollis have declared no conflicts of interest. The study was supported by the National Institutes of Health Grant R01 NS041435, the Kenneth and Claudia Silverman Family Foundation, and an American Medical Association Foundation Seed Grant.