U.S. Some clues for understanding depression have been discovered by New York University scientists who have identified a candidate biological marker. As a new study, immune cell aging appears to be linked to particular emotional and mental symptoms of depression.
The study, published in The Journals of Gerontology, Series A: Biological Sciences and Medical Sciences in May 2026, investigated a kind of white blood cell called monocytes that are known to be crucial to immune defence and inflammation. The researchers found a relationship between faster biological aging of monocytes and sensation of helplessness, failure, and anhedonia (reduced ability to feel pleasure).
All cells can age at a molecular level too, which may not always match the individual’s age in years. Such changes can be measured via epigenetic clocks, by analyzing chemical modifications to DNA that represent certain shifts in cell activity.
In this study, the research team used blood samples to look at two measures of biological aging: one that was not specific to any cell type or tissue and the other that focused on a type of immune cell called a monocyte.
These findings showed a significant correlation between accelerated aging of monocytes and symptoms of depression that aren’t linked to the body. The other cell and tissue type measure of aging was not related to the depression symptoms.
These may include both physical and mental and emotional symptoms. Some feel overwhelmed by feelings of loss or despair. Others might feel sluggish, have fluctuations in their appetite, difficulty focusing or a general disinterest in things that normally appeal to them.
More exactly, the NYU research showed that monocyte biological aging was related to non-somatic symptoms or symptoms that aren’t focused on the body. Anhedonia, the inability to experience pleasure, was quite a bit correlated with greater monocyte aging in the entire sample.
That difference may be significant since physical symptoms can also have alternative diagnoses. For individuals living with a chronic condition, such as HIV, fatigue, or changes in energy may have many different causes. In the future, biological markers that offer complementary data to emotional symptoms may help to identify these distinctions.
But the findings do not prove aging immune cells are responsible for depression. It’s possible there are other biological, psychological, and environmental factors at play, and it’s still unclear how the immune cells and depression are connected.
Currently depression is diagnosed based on clinical exams and conversations about symptoms, how long they last and how they affect daily life. A doctor may also do blood tests to rule out other illnesses or conditions that could be causing the symptoms, but no standard blood test can diagnose depression on its own.
Over time, a biological marker might also add to these measures. It could help researchers distinguish subgroups of people with depression based on biological differences, better understand variations in symptoms or explore whether some subgroups of people are more or less likely to benefit from a certain treatment.
Still, the authors also believe monocyte aging could work as a candidate for future research. That being said, the study was limited to a specific sample of women, so the results may not be generalizable to men, other age groups or everyone with depression.