Restricting calories keeps immune system young.

Drastic limits on calorie consumption starting early in a monkey's life seemed to delay aging of the animal's immune systems in new research.

Numerous studies have found that calorie restriction can extend the life span of organisms such as yeast, worms, fruit flies, and mice. However, scientists don't know how caloric restriction lengthens life.

Janko Nikolich-Zugieh of the Oregon Health and Science University in Beaverton, Ore., and his colleagues suspected that the immune system plays an important role. They worked with two groups of rhesus macaques. Starting just after puberty, monkeys in one of the groups were fed about a third fewer calories than were monkeys in the other group. When the monkeys were between 19 and 23 years old, the researchers monitored differences in immune function between the groups for 42 months.

The immune systems of monkeys on the restricted diets appeared to have aged significantly slower than those of monkeys eating the typical number of calories, the team reports in an upcoming Proceedings of the National Academy of Sciences. For example, when the researchers took immune cells called T cells from both groups and placed them in lab dishes with antibodies that trigger an immune response, cells from the calorie-restricted monkeys went through about a third more divisions than did cells from monkeys in the other group. Cells from the calorie-restricted animals also produced fewer chemicals that cause inflammation.

Nikolich-Zugich cautions that elderly people shouldn't cut back on calories to preserve their immune systems. However, he suggests that in the future, researchers might develop drugs that mimic caloric restriction's beneficial effects.--C.B.