For many years, scientists believed that the thymus was mainly important during childhood. This small organ, located in the upper chest behind the breastbone, helps train immune cells when people are young.
After puberty, the thymus gradually shrinks, and many researchers assumed it became much less important later in life.
New research is now challenging that idea. Scientists from Mass General Brigham have found evidence that the thymus may continue to play a major role throughout adulthood. Their findings suggest that people with healthier thymuses may live longer, have lower risks of serious diseases, and respond better to certain cancer treatments.
The research was published in two studies appearing in the same issue of Nature. Together, the findings suggest that the thymus deserves much more attention than it has received in the past.
The thymus helps produce and train T cells, a special type of immune cell that protects the body from infections, abnormal cells, and diseases. A healthy immune system relies on a diverse collection of T cells that can recognize many different threats. As the thymus shrinks with age, the body produces fewer new T cells, which may weaken the immune system over time.
Previous studies hinted that declining immune function may be linked to aging and disease, but most of those studies were small and focused on blood tests. The new research took a much larger approach.
The scientists analyzed information from more than 25,000 adults who participated in a national lung cancer screening study. They also examined data from more than 2,500 people in the famous Framingham Heart Study, which has tracked health and disease in American adults for decades.
Using artificial intelligence, the researchers studied routine CT scans and examined the size, structure, and appearance of each person’s thymus. From this information, they created a thymic health score that reflected how healthy the organ appeared.
The results were striking. People with healthier thymuses experienced much better health outcomes than those with less healthy thymuses.
Compared with people who had poorer thymic health, those with healthier thymuses had about a 50 percent lower risk of dying from any cause. They also had a 63 percent lower risk of dying from cardiovascular disease and a 36 percent lower risk of developing lung cancer.
Importantly, these relationships remained strong even after researchers adjusted for age and other factors that could influence health. This suggests that thymic health itself may play an important role.
The researchers believe that when thymic health declines, the body may lose some of its ability to produce diverse T cells. This could make it harder for the immune system to recognize and respond to new threats such as cancer cells, infections, and other diseases.
The study also identified several factors associated with poorer thymic health. People who smoked, carried excess body weight, or had higher levels of chronic inflammation tended to have less healthy thymuses. These findings suggest that lifestyle and long-term inflammation may influence how well the immune system ages.
In a second study, researchers explored whether thymic health could affect cancer treatment outcomes. They examined more than 1,200 cancer patients who received immunotherapy, a modern treatment that helps the immune system attack cancer.
Patients with healthier thymuses were more likely to benefit from treatment. They had a 37 percent lower risk of cancer progression and a 44 percent lower risk of death compared with patients who had poorer thymic health.
This finding may help explain why some people respond very well to immunotherapy while others do not. The thymus could be an important factor influencing the strength and effectiveness of the immune response.
Although the findings are exciting, the researchers emphasize that more work is needed. The imaging method used in the study is not yet ready for routine use in hospitals, and the research cannot prove that improving thymic health will directly improve health outcomes.
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Source: Mass General Brigham.
