A new study has found that faster aging in one type of immune cell was linked to the hopelessness and loss of pleasure that can mark depression.
The finding points toward a possible blood marker for depression, which doctors still diagnose largely through patient-reported symptoms.
A signal in blood
In stored blood samples from a long-running women’s health cohort, the signal appeared inside white blood cells involved in the body’s early immune response.
By comparing those cells’ biological age with symptom reports, Nicole Beaulieu Perez, Ph.D., at New York University (NYU), tied older-looking monocytes to mood and cognitive symptoms, not fatigue or appetite changes.
The same pattern held in women with HIV and women without it, narrowing the finding beyond one chronic illness or one patient group.
Because depression often overlaps with physical symptoms, researchers still need to separate meaningful mood signals from the body’s ordinary fluctuations.
Symptoms blur together
Medical teams use depression screening – standard questions that flag mood changes – to help diagnose depression and judge severity, but the process still depends on what a person can describe.
Symptoms can hide in plain sight when tiredness, sleep trouble, or appetite changes look like stress, another illness, or medication effects.
Recent data from the Centers for Disease Control and Prevention (CDC), the federal public health agency, show that 19% of U.S. adults said a health professional had diagnosed them with a depressive disorder in 2024.
Clues inside blood cells
Monocytes sit in the bloodstream and move into tissues when the immune system senses trouble.
Inflammation changes their behavior, and those changes may leave chemical marks that reveal stress inside the body.
That fits the clue Perez saw: the older-looking cells lined up with emotional pain, not with the physical complaints that often complicate diagnosis.
“Our study reveals unique biological underpinnings of mental health that are often obscured by broad diagnostic categories,” said Perez.
Measuring cell aging
Aging researchers use epigenetic clocks to read chemical tags on DNA and estimate how old cells appear.
One broad clock scanned many tissues and cell types, which can blur a signal that belongs to one immune cell.
Perez’s team also used a monocyte-focused clock, and that narrower reading caught the depression-related pattern.
Inside the cohort
Data came from the Women’s Interagency HIV Study, a federally funded project begun in 1993 to track how HIV affects women.
Investigators analyzed blood and symptom data from 440 participants: 261 women living with HIV and 179 women without HIV.
Nearly half of both groups identified as Hispanic, and about one-third or more as Black; that diversity is notable because biomarker studies often use narrower samples.
Even so, the findings apply only to the women studied, not automatically to men, children, or people outside similar research settings.
Physical symptoms differ
Survey answers separated physical complaints from non-somatic symptoms – mood and cognitive problems that are not mainly body sensations.
The strongest tie appeared in loss of pleasure, hopelessness, and feelings of failure, signs that can appear before a person names depression.
By contrast, fatigue and restlessness did not line up with the monocyte aging signal. The finding suggests emotional symptoms may slip past notice more easily than physical changes such as sleep or appetite disruption.
Depression and HIV
Among women with HIV, untreated depression can disturb antiretroviral medication – daily treatment that controls the virus – and disrupt care.
Fatigue is common in many chronic illnesses, so body-heavy scores can send doctors down the wrong path.
“For women with HIV who may be experiencing depression, we want to better understand what’s going on and catch it earlier so that it doesn’t harm their whole overall health,” said Perez.
Her team’s finding points to mood and cognitive symptoms as the place where the blood signal may be most useful.
Promise and caution
The result does not mean a clinic can order this test tomorrow. Scientists still need to see whether monocyte aging rises before symptoms appear, falls after treatment, or predicts which patients will worsen.
The key limitation is that the study shows association, not proof of cause: aging immune cells may not cause depression.
Still, a cell-specific blood signal gives researchers a sharper target than a broad diagnosis.
Toward precision care
Mental health care often moves by trial and adjustment after first treatment fails.
A useful biomarker could eventually help clinicians match patients with therapies sooner, if future studies connect the signal to treatment response.
That would not make depression less personal, but it could make care less dependent on waiting for symptoms to become severe.
Personalized care ahead
A blood-based signal tied to mood and cognitive symptoms would give doctors one more way to spot depression early, especially in patients whose physical symptoms already have other explanations.
Larger studies must test whether the marker works across more groups, how stable it remains over time, and whether it improves care enough to justify clinical use.
The study is published in The Journals of Gerontology: Series A.
—–
Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.
Check us out on EarthSnap , a free app brought to you by Eric Ralls and Earth.com.
—–