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.
