Age-related immune system decline slowed by antioxidants

The thymus is an organ that produces T lymphocytes – white blood cells that are crucial to the immune system.

New research has demonstrated how the aging process damages the immune system, while showing how antioxidants in the diet could slow the build-up of this damage.

Findings from the study, published in Cell Reports, also lend support to the “free-radical theory” of aging, whereby reactive oxygen species such as hydrogen peroxide that are produced by normal metabolism cause damage to cells. This damage contributes to both aging and age-related diseases.

The study was conducted by researchers from The Scripps Research Institute (TSRI) who focused their attention on an organ called the thymus that is responsible for the production of T lymphocytes – also referred to as T cells.

T cells are white blood cells that control the body’s immune response. These cells are continuously lost, and it is the job of the thymus – located between the lungs – to replenish them, enabling the body to respond to new infections. However, the thymus is unable to continuously produce high levels of T cells.

“The thymus begins to atrophy rapidly in very early adulthood, simultaneously losing its function,” explains study author Dr. Howard Petrie. “This new study shows for the first time a mechanism for the long-suspected connection between normal immune function and antioxidants.”

Antioxidants are substances that could prevent or delay damage to cells. Examples include beta-carotene, vitamin C and vitamin E. They can often be found in fruits and vegetables and are also available in the form of supplements.

The researchers set out to explore the mechanisms behind the connection by developing a computational approach they could use to assess gene activity in two types of thymus cell in mice – stromal cells and lymphoid cells.

In the stromal cells, they observed that a deficiency in an antioxidant enzyme called catalase led to the production of reactive oxygen species through metabolism, which in turn sped up the rate at which damage occurred.

COMMON DIETARY ANTIOXIDANTS FOUND TO PRESERVE SIZE OF THE THYMUS

The researchers then tested the role of this antioxidant by increasing catalase levels in genetically altered animal models. By doing this, they were able to maintain the size of the thymus for a longer period.

In addition, the researchers were also able to preserve the size of the thymus in animals by giving them two common dietary antioxidants – including vitamin C.

The question of why the thymus decreases in size more rapidly than other body tissues remains unanswered, however. Dr. Petrie says that while other research has demonstrated the thymus is responsive to sex hormones, their new study shows that its aging process is the same as in other tissues.

“However, the process is accelerated in the thymus by a deficiency in the essential protective effects of catalase, which is found at higher levels in almost all other body tissues,” he continues.

The researchers also point out that while increasing catalase levels in stromal cells preserved the size of the thymus for a longer period, it did not prevent it from atrophying – as yet, there is no way to completely halt metabolic damage accumulated over time.