THURSDAY, Feb. 23 (HealthDay News) — Discovery of the molecular mechanism that the body uses to fight off tuberculosis could open the way to use of ordinary vitamin supplements to help prevent the disease, researchers report.
The finding also helps explain why blacks are more vulnerable than whites to tuberculosis and why they develop more severe cases when infected, according to a study in the Feb. 23 online issue of Science.
The story starts about a decade ago, when research revealed that the immune system of fruit flies produces a protein that attacks bacteria and fungi, explained study author Dr. Robert L. Modlin, chief of dermatology at the University of California, Los Angeles.
“In 1999, it became clear that there were equivalents in humans, a family of proteins,” Modlin said. “Each recognizes a defined biochemical from a bacterium or virus.”
Studies showed that in mice, the defense involved production of nitric oxide to fight infection. However, that was not found to happen in human cells, Modlin said.
Four years of work led to the finding that the human defense mechanism involves vitamin D, he said. White blood cells are stimulated to convert ordinary vitamin D — which is produced, in large part, by exposure to sunlight — into an active form that is used to make a protein that kills the tuberculosis bacteria.
“Our other main finding was that African-Americans, who are known to be more susceptible to tuberculosis, have lower levels of vitamin D in their blood,” Modlin said. Melanin, the pigment that darkens skin, absorbs the ultraviolet rays of sunlight, reducing vitamin D production in blacks, he explained.
Cells grown in blood serum from black individuals produced 63 percent less of the bacteria-fighting protein than those grown in blood serum from white people. Adding vitamin D to the cultures increased production of the protein, Modlin said.
One question raised by the discovery is whether giving vitamin D to humans can do the same thing, he said, adding, “Were hoping this paper will raise interest in that.”
If the vitamin does have a protective effect, “a vitamin D supplement I think is the way to go,” Modlin said. As a dermatologist, he noted, he is acutely aware of the damage that can be done by overexposure to sunlight.
However, “I can’t recommend that people take vitamin D supplements yet,” Modlin said. “We need to do more studies.” His group is doing studies along that line, looking at “what effects vitamin D might have on the immune system.”
There’s a possibility that the work might have implications beyond tuberculosis, Modlin said. “Our results indicate we have much yet to learn about human immune responses to infections,” he said.