Vitamin D Critical to Triggering Immune Defenses

Danish scientists have discovered that Vitamin D is crucial to activating humans' immune defenses, and that without sufficient intake of the vitamin, the killer cells of the immune system--T cells--will not be able to react to and fight off serious infections in the body.

For T cells to detect and destroy foreign pathogens such as clumps of bacteria or viruses, the cells must first be triggered into action and transform from inactive and harmless immune cells into killer cells that are primed to seek out and destroy all traces of a foreign pathogen.

The researchers found that the T cells rely on vitamin D in order to activate and they would remain dormant, "naïve" to the possibility of attack if vitamin D were lacking in the blood. "We have discovered that the first stage in the activation of a T cell involves vitamin D, explained Prof. Carsten Geisler, from the department of international health, immunology, and microbiology at the University of Copenhagen (Denmark). When a T cell is exposed to a foreign pathogen, it has an immediate biochemical reaction and extends a signaling device or "antenna” known as a vitamin D receptor, with which it searches for vitamin D. This means that the T cell must have vitamin D or activation of the cell will cease. If the T cells cannot find enough vitamin D in the blood, they won't even begin to mobilize.”

T cells that are successfully activated convert into one of two types of immune cell. Either they become killer cells that will attack and destroy all cells carrying traces of a foreign pathogen or they become helper cells that assist the immune system in gaining "memory.” The helper cells send messages to the immune system, passing on information about the pathogen so that the immune system can recognize and remember it at their next encounter and launch a more efficient and enhanced immune response. T cells form part of the adaptive immune system, which means that they function by teaching the immune system to recognize and adapt to constantly changing threats.

For the research team, identifying the role of vitamin D in the activation of T cells has been a major breakthrough. "Scientists have known for a long time that vitamin D is important for calcium absorption and the vitamin has also been implicated in diseases such as cancer and multiple sclerosis, but what we didn't realize is how crucial vitamin D is for actually activating the immune system, which we know now.”

These findings, the scientists believe, provide much needed data about the immune system, and will help them control the immune response. This is significant not only in fighting disease but also in dealing with anti-immune reactions of the body and the rejection of transplanted organs. Active T cells multiply at an explosive rate and can create an inflammatory environment with serious consequences for the body. After organ transplants, for instance T cells can attack the donor organ as a "foreign invader.” In autoimmune disease, hypersensitive T cells mistake fragments of the body's own cells for foreign pathogens, leading to the body launching an attack upon itself.

The scientists were also able to track the biochemical sequence of the transformation of an inactive T cell to an active cell, and thus they could intervene at several points to modulate the immune response. Inactive (naïve) T cells crucially contain neither the vitamin D receptor nor a specific molecule (phospholipase C-gamma 1 [PLCgamma 1]) that would enable the cell to deliver an antigen specific response.

The findings continued Prof. Geisler, "could help us to combat infectious diseases and global epidemics. They will be of particular use when developing new vaccines, which function precisely on the basis of both training our immune systems to react and suppressing the body's natural defenses in situations where this is important--as is the case with organ transplants and autoimmune disease.”

Most vitamin D is produced as a natural byproduct of the skin's exposure to sunlight. It can also be found in fish liver oil, eggs, and fatty fish such as salmon, herring, and mackerel, or it can be taken as a dietary supplement.

The findings were published March 7, 2010, in the journal Nature Immunology.

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