Innate immunity is the natural ability of the body to fight specific molecules found on microorganisms. This progressive ability has been achieved through the evolutionary process. It has been known from previous studies that mice effectively combat the tubercle bacillus by production of nitric oxide in macrophages, the so-called scavenger cells of the immune system. This mechanism is however poorly understood in human beings.
Human macrophages have a set of receptors (toll like receptors) that contribute to innate immunity. It ahs now been shown that this may be to a large extent dependent on absorption, storage and utilization of Vitamin D. Stimulation of toll like receptors by specific molecules of the tubercle bacillus activates an enzyme (Cyp27B1) and Vitamin D receptors, resulting in conversion of inactive form of the vitamin to active form.
This dual activation induces cleavage of a preexistent protein to cathelicidin (a small peptide), capable of destroying TB bacilli in a test tube. This vitamin D production effect cannot take place without exposure to ultraviolet light.
African Americans have high levels of melanin, a skin pigment that absorbs UV light. This limits the intrinsic ability of vitamin D production. Consistent with the theory, in vitro culture of cells of African Americans were found to produce lowered levels of cathelicin (63%), compared to those of the whites.
The result of the present study has enabled scientists to unravel two major mysteries associated with Tuberculosis. One, the diversity of the mice and human anti-bacterial mechanism, and two, the increased susceptibility of Africans and Asian to TB. The researchers have highlighted the need for clinical trials to investigate the beneficial effect of Vitamin D supplementation in prevention of TB.
If successful, we might perhaps be one day able to modify an individual's susceptibility to TB, more specifically in the vulnerable population by supplementation of vitamin either through diet or a cheap vitamin pill.