Scientists at the University of Copenhagen have discovered that Vitamin D is crucial to activating our 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 kill 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 threat if vitamin D is lacking in the blood. In order for the specialized immune cells (T cells) to protect the body from dangerous viruses or bacteria, the T cells must first be exposed to traces of the foreign pathogen. This occurs when they are presented by other immune cells in the body (known as macrophages) with suspicious 'cell fragments' or 'traces' of the pathogen. The T cells then bind to the fragment and divide and multiply into hundreds of identical cells that are all focused on the same pathogen type. The sequence of chemical changes that the T cells undergo enables them to both be 'sensitized to' and able to deliver a targeted immune response.

Professor Carsten Geisler from the Department of International Health, Immunology and Microbiology explains that "when a T cell is exposed to a foreign pathogen, it 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 transform into one of two types of immune cell. They either 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 acquiring "memory." The helper cells send messages to the immune system, passing on knowledge about the pathogen so that the immune system can recognize and remember it at their next encounter. 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.

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