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Youthful Immune System in Old Age Can Apparently Be Harmful
Immune defenses that function in old age as they did in youth are considered desirable. However, a recent study shows that a youthful immune system in older age can also cause harm.
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As part of the natural aging process, the human immune system weakens over the years.1 One reason for increased susceptibility to infections in old age is that fewer new T-cells are produced, as the thymus—the maturation organ for T-cells—shrinks. T-cells recognize and destroy harmful cells in the body and activate other parts of the immune system. Because the immune system weakens with age, people with an active immune system seem to have an advantage. But: This supposed immune youthfulness can apparently also be harmful.
Also interesting: Certain diets could cripple the immune system
Details of the Study
A research team from the U.S. Mayo Clinic found, after evaluating health records of about 22 million people, that many autoimmune diseases only appear in older age. At the same time, it is known that general immune defense weakens with age.2 From this paradox, the researchers concluded that the immune system in older age is not just still active but sometimes possibly too active. In autoimmune diseases, a malfunction of the immune system is known to occur, leading the body to attack its own tissue.
Researchers Found Immune Cells in Diseased Tissue of Giant Cell Arteritis Patients
In the next step, the scientists examined aortic sections from more than 100 patients over 50 years old, who are being treated for giant cell arteritis at the U.S. Mayo Clinic. This is a rarer, inflammatory autoimmune disease of the large and medium arteries, often affecting the cranial arteries and aorta. The Mayo Clinic is globally renowned for its expertise in complex diseases, including giant cell arteritis (GCA).3
The researchers found an increased presence of specialized immune cells, known as stem cell-like T-cells, in the diseased tissue of the patients. To recap: The previously mentioned T-cells are normally responsible for fighting infections as part of the immune system. These special T-cells behave similarly to T-cells in young organisms, as they can renew themselves and continuously produce new defense cells. However, in the presence of giant cell arteritis, this seemingly beneficial effect appears to be misguided. Instead of protecting the body from invaders, these cells continuously supply new T-cells that attack the blood vessels of those affected. Their efficiency thus causes significant damage.
How a Youthful Immune System Attacks Its Own Cells
As people age, more new, unusual protein forms accumulate in the body, the study authors write: so-called neoantigens. The immune system has not yet developed tolerance to these proteins. 'This is likely to inevitably lead to an increase in autoimmune diseases in old age,' the study continues. Normally, the immune system prevents these neoantigens from attacking its own cells. However, with age, these control mechanisms can be disrupted—a possible explanation for why autoimmune diseases occur more frequently in old age.
The study's results suggest that autoimmune diseases in old age are not solely a result of weaker defenses. In summary, a combination of 'youthful' T-cells and an increasing number of new antigens seems to lead to the immune system being unable to stop certain inflammations in old age. Part of the immune system remains overly efficient, and this can be harmful to the aging body.
Significance of the Study and Limitations
The observations could offer new perspectives for medical practice—at least if the findings are confirmed in further studies. The research team plans to develop diagnostic tests that could potentially predict autoimmune diseases later in life based on the high activity of immune stem cells in currently healthy individuals. For study author Dr. Jörg Goronzy, these findings are already significant. 'Contrary to popular belief, an immune system that ages with the body does have advantages,' he explains in a press release.3 He suggests that moderate aging of the immune system can be protective, as it dampens the response to one's own cells.
It should be noted that the study is based on existing studies. No new experiments were conducted; rather, existing data were interpreted. This limitation may slightly affect the reliability of the results. Additionally, only tissue from giant cell arteritis patients was analyzed. Whether the observations can be applied to other autoimmune pathologies remains unclear—likewise, how the specific, stem cell-like T-cells that are beneficial for tissue repair differ from those that contribute to autoimmune pathology in older patients. FITBOOK has reached out to the authors with these and other questions. A response is still pending.
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