Understanding Vitamin A
attack by some food-poisoning organisms but not, for example, the
common cold? Researchers in the US try to unravel the mystery.
US researchers, trying to understand why vitamin A helps fight certain diseases and not others, say that the vitamin influences the types and amounts of immune cells and molecules produced in response to attack.
Vitamin A can aid the immune system in fighting certain infections and inflammations, such as measles and 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, say researchers at the ARS Western Human Nutrition Research Center in Davis, California.
The team is trying to explain why vitamin A interacts in different ways with the immune system. Findings from the research may lead to promotion of vitamin A-rich foods as immune-boosters. Such foods include beef, chicken, turkey, pumpkin, carrots, spinach, collard greens and tomato products.
"Our team has shown that vitamin A influences the types and amounts of immune cells - such as T-helper cells - and immune system molecules, called interferons and interleukins, that your body produces in response to infection," said research physiologist Charles B. Stephensen.
"These cells and molecules have specialised jobs. That means the types and amounts of each that your body mobilises can strongly affect how slowly or quickly you overcome a particular infection or inflammation."
In an early study, Stephensen and his colleagues 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. Their work showed 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, according to the researchers, because T-2 helper cells apparently are more proficient in fighting some pathogens than others.
Stephensen explained that although full understanding of the specialisation of the helper cells is limited, in general Th1 cells seem to be of most use in fighting viral infections, such as HIV, while Th2 cells apparently have the lead role in defending against certain bacteria or intestinal parasites, like roundworms.
In humans, that difference could strongly affect how quickly the body is able to overcome a particular pathogen. They plan to repeat these early tests with laboratory mice - not just their cells, as used in the earlier study. Later they may follow up with studies of healthy adult volunteers.
Details of this research were published in the March 2003 issue of the Agricultural Research magazine.
