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OHSU Research Shows Reduced Caloric Intake Delays Immune System Aging

   Portland, Ore.

Researchers at the Vaccine and Gene Therapy Institute at Oregon Health & Science University have demonstrated that a reduced calorie diet delays aging of the immune system in monkeys. This is the first such study conducted in nonhuman primates to demonstrate this connection. The research is printed in this week's online edition of the Proceedings of the National Academies of Science.

Recent research in monkeys at the University of Wisconsin and the National Institute on Aging has suggested that a reduced calorie diet may increase lifespan. In addition, past studies in rodents have shown that similar diets can delay aging of the immune system. However, until now, it was unclear whether caloric restriction could impact the immune systems of long-lived animals and primates such as monkeys, apes and man.

"Understanding the aging immune system and ways to maintain robust disease protection is a major priority for health researchers," explained Janko Nikolich-Zugich, Ph.D., a senior scientist at the VGTI and the Oregon National Primate Research Center; and a professor of molecular microbiology and immunology in the OHSU School of Medicine. "Due to longer life spans and the availability of cutting-edge medical treatments, the American population as a whole is aging. However, because the immune system typically weakens late in life, a greater number of Americans are more susceptible to infectious diseases such as the flu, which currently kills about 36,000 U.S. citizens annually."

To conduct the research, the researchers studied 42 adult rhesus macaque monkeys. Some of the animals were fed a health sufficient, reduced calorie diet while other animals received a more traditional monkey diet. The immune systems of the animals were then monitored over a 42 month period.

During this time, researchers tracked two forms of T cells. T cells are white blood cells that detect and fight disease. The first kind of T cells that the researchers tracked were naive T cells. These cells are called naive because they were not yet exposed to disease-causing microbes. The role of these cells is to detect and fight off diseases not yet encountered by the body.

The researchers also measured levels of memory T cells. Unlike naive T cells, memory T cells have already encountered disease-causing microbes and are therefore programmed to fend off these microbes when and if they attack again. While both forms of T cells are important, a reduction in the levels of naive T cells occurs naturally in the aging process and leads to a weakening of the body's immune system. 

The results of the researchers' analysis showed that the monkeys on the reduced-calorie diet preserved higher levels of naive T cells longer than animals on a traditional monkey diet. Furthermore, the reduced calorie diet also improved T cell function and reduced the degradation of memory T cells.  In summary, this means that the caloric-restricted animals were better protected against a larger number of diseases, which could contribute to longer life spans.

"In addition to delayed aging of the immune system, a reduced calorie diet also appears to have a significant impact on other health issues," added Nikolich-Zugich, lead researcher on this study. "Preliminary studies by other groups in nonhuman primates suggest that caloric restriction can reduce the occurrence of diabetes, cardiovascular disease and cancer."

In regards to their research, Nikolich-Zugich and his colleagues now hope to learn more about the reasons why a reduced calorie diet can lengthen the life of the immune system. The researchers hope that this new information will provide possible therapies or treatments to better protect the country's aging population.

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