Detectives Probe Secrets of Vitamin A
By Marcia Wood
March 28, 2003
Vitamin A can aid the immune system in
fighting certain infections and inflammations. This essential nutrient, for
example, can help clobber infections caused by some food-poisoning organisms.
However, in the case of pneumonia--and perhaps asthma and the common cold,
as well--vitamin A may not be as helpful.
At the ARS Western Human Nutrition
Research Center in Davis, Calif., innovative studies by research
physiologist Charles B. Stephensen are helping solve the puzzle of why vitamin
A interacts in these differing ways with the immune system. Findings from the
research may lead to ways to capitalize on the ability of vitamin A-rich foods
to boost the immune system.
Foods that provide Vitamin A include beef, chicken, turkey, sweet potatoes,
pumpkin, carrots, spinach, collard greens and tomato products.
Experiments by Stephensen and his university and corporate colleagues are
revealing more clues about vitamin A's influence on the types and amounts of
beneficial cells and compounds that the immune system produces in response to
In one early study, the scientists supplied animal immune cells with
adequate amounts of a form of vitamin A called 9-cis retinoic acid, and exposed
the cells to a simulated attack. This work showed--for the first time--that
more of the cells quickly evolved into what are known as T-2 helper cells than
into T-1 helper cells. This difference is important, because T-2 helper cells
apparently are more proficient in fighting some pathogens than others.
In humans, that difference could strongly affect how quickly the body is
able to overcome a particular pathogen.
The researchers used mouse immune cells for these petri dish tests. They
plan to repeat these tests with laboratory mice--not just their cells.
Depending on the outcome, they expect to follow up with studies of healthy
Details are in Agricultural Research magazine.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.