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A hormone that naturally declines as we grow older may play a key role in the chronic inflammation linked to cancer and other age-related diseases, according to new research in mice.
The hormone, called thymulin, is produced by the thymus, a small organ behind the breastbone that helps train the body’s immune system. Researchers at the Keck School of Medicine of USC found that as thymulin levels fall with age, inflammation rises. Restoring the hormone in older mice reduced signs of age-related inflammation and improved the animals’ ability to fight cancer.
The findings, published in Nature Communications, point to a previously unknown connection between aging, inflammation and the immune system.
Scientists have long known that older adults tend to experience a persistent, low-level form of inflammation known as inflammaging. This chronic inflammation has been linked to a range of serious conditions, including heart disease, cancer, metabolic disorders and neurodegenerative diseases. What has remained less clear is why inflammation increases with age in the first place.
The new study suggests the thymus may be part of the answer.
Although the thymus is best known for producing immune cells called T-cells, the researchers found that one of the organ’s hormones also appears to help keep inflammation under control. Their experiments showed that thymulin regulates cytokines, signaling proteins that can trigger inflammatory responses throughout the body.
As thymulin levels declined, cytokine levels increased.
To uncover the hormone’s role, researchers used an unusual technique that pairs an older mouse with a younger one so the two animals share a blood supply. The approach reduced inflammation in the older mice, suggesting that factors circulating in young blood might help counter some effects of aging.
The team then analyzed human blood samples and mouse models while searching for genes linked to aging and longevity. That investigation repeatedly pointed them back to the thymus, leading to the discovery of thymulin’s apparent role in regulating inflammation.
The hormone’s impact extended beyond inflammation alone.
In older mice with cancer, increasing thymulin levels boosted immune responses against tumors and improved survival. The treatment also enhanced the effectiveness of anti-PD-1/PD-L1 therapy, a form of immunotherapy that helps the immune system recognize and attack cancer cells.
The results suggest that the age-related loss of thymulin may contribute not only to chronic inflammation but also to changes in immune function that occur later in life.
Importantly, the research was conducted in mice, and the study does not show that thymulin prevents or treats cancer in people. Instead, the findings identify a biological pathway that researchers believe deserves further investigation.
According to lead author Dr. Fumito Ito, the work provides the first evidence that a substance naturally produced by the thymus declines with age and can reverse age-related inflammation.
The discovery also opens the door to additional questions. Researchers plan to explore whether thymulin influences how tumors form and spread and whether it plays a role in other conditions linked to inflammaging, including diabetes, chronic kidney disease and Alzheimer’s disease.
Prof. Ercüment Ovalı, a hematologist, stem cell biologist and director of Acıbadem Labcell who was not involved in the research, told Newsweek that approaches aimed at targeting immune aging could eventually become relevant for treating age-related diseases, particularly cancer, where older patients often face both a higher cancer risk and less effective immune responses. However, he cautioned that such strategies remain at the preclinical stage and require further study before they can be translated into treatments.
Cancer treatment outcomes, according to Ovalı, depend on more than the tumor itself and the drugs used against it. The biological condition of a patient’s immune system can also influence how effective treatment is, highlighting the importance of considering immune function alongside cancer therapies.
The findings may have implications for aging research more broadly. Scientists often rely on younger laboratory animals because they are easier and less expensive to study, but the authors argue that doing so may underestimate the effects of chronic inflammation associated with aging.
Ovalı noted that one of the key unanswered questions is whether thymulin levels actually decline with age in humans, something that will need to be established through clinical research.
For now, the study suggests that a hormone produced by a little-known organ could be an important piece of the puzzle connecting aging, inflammation and disease. Whether the same mechanism operates in humans—and whether boosting thymulin could one day have clinical benefits—remains to be determined.
Reference:
In addition to Ito, the study’s other authors are Hisashi Kanemaru, Steven Luong, Yuta Yamamoto and Yukari Mizukami from the Department of Surgery, Keck School of Medicine of USC, University of Southern California.
This work was supported by the National Cancer Institute of the National Institutes of Health [P30CA014089, R01CA255240, R01CA272827, R01CA316597] and involved the use of USC’s Flow Cytometry and Immune Monitoring Core.
DOI: 10.1038/s41467-026-75383-0
Contact Newsweek editors on this story: Kara Dolman and Sam Wilson.
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