New Immune Marker Research on Ketamine for Treatment-Resistant Depression (2026 Study)
IL-15 and IL-7: the immune markers a new 2026 study looked at beyond the standard inflammation markers CRP and IL-6, and how they tracked with ketamine response in depression
A new study published in Molecular Psychiatry found that the people who responded to ketamine treatment for depression shared an immune signature built from markers researchers rarely look at, and it was visible in their blood before treatment started.
The research came out of MD Anderson Cancer Center and the National Institute of Mental Health, and the same paper tested psilocybin and LSD in laboratory-grown neurons and found they act on several of the same immune pathways ketamine does.
The markers: IL-7 and IL-15.
If you follow my practice, you know I talk constantly about inflammation (part of the immune system) as a driver of both chronic pain and depression. I have written about how pain, depression, and inflammation are connected and about ketamine, NAD+, and the kynurenine pathway. Those conversations have centered on CRP and IL-6, because that is where the research has been for the past decade.
IL-7 and IL-15 are not those markers. They are not measures of inflammation at all. They do a different job in the immune system: deciding how many immune cells the body keeps in circulation, day to day, whether or not anything is wrong.
One clarification: The signature does not mean only people who have it can respond to ketamine. It means that within this group, it tracked with who did.
Key points from the new ketamine, depression, and immune system study (2026)
Ketamine responders had lower IL-15 pathway activity and higher B-cell signaling before treatment than non-responders.
Both measures reversed in the people whose treatment-resistant depression improved.
IL-7 and IL-15 are not inflammation markers like CRP or IL-6. They regulate how the immune system maintains itself.
IL-7 levels in blood lined up with brain activity on a scan, measured in the same people at the same time. A blood draw could eventually stand in for a scan.
Real patients received ketamine in this study. Nobody received psilocybin or LSD. The psychedelic comparison was a separate experiment run on neurons grown in a lab dish.
Patients in this study received ketamine. The psilocybin and LSD results came from a separate experiment on neurons grown in a lab dish, so no participant received a psychedelic.
What did the 2026 Molecular Psychiatry study on ketamine and immune markers find?
The study came in two halves: a trial in actual patients, and a separate experiment in a laboratory.
In the patients: Researchers gave a single intravenous dose of ketamine (0.5 mg/kg) or a placebo to adults with treatment-resistant depression and to healthy volunteers, then measured three things:
gene activity in blood
immune proteins in plasma
brain electrical activity on a magnetoencephalography (MEG) scanner.
Responders and non-responders already differed before the infusion. Responders started with lower IL-15 pathway activity and higher B-cell signaling, and both reversed after treatment in the people who improved.
In the lab: The team grew neurons from participants' own cells and exposed those cells to four drugs: ketamine, its metabolite (2R,6R)-hydroxynorketamine, LSD, and psilocybin. All four converged on overlapping immune pathways despite acting on different receptors, with IL-15 and MCP-1 as the central hubs.
In short: the ketamine findings came from people. The psychedelic findings came from cells in a dish.
How did researchers link blood immune markers to brain activity after ketamine treatment?
Most studies measure blood or brain and infer the connection between them. This one measured both in the same people, at the same time.
A person's IL-7 level in plasma lined up with their gamma power on MEG, a measure of fast brain oscillations. Higher IL-7, higher gamma. The relationship was strongest across subcortical regions in the depressed group, and after ketamine it flipped, alongside broad gamma reductions in the default mode network, the circuit tied to self-referential rumination.
That correlation is the practical part: if a number from a blood draw reliably reflects what a scanner would show, the blood draw could eventually replace the scanner.
What are IL-7 and IL-15, and how do they differ from inflammation markers like CRP and IL-6 in depression?
Most previous research on depression and the immune system measured CRP, IL-6, and TNF-alpha. Those are smoke alarms. They go off when something is burning: an infection, an injury, an autoimmune flare. The theory was that depression involves a body that is chronically smoldering and that the smoke reaches the brain.
If CRP, IL-6, and TNF-alpha are smoke alarms, IL-7 and IL-15 are the thermostat.
They (are supposed to) keep the immune system's cell populations at the right levels, deciding how many of each type to hold in circulation. When they are off, nothing is burning. The setting is just wrong.
This evolves the question beyond "Is the patient inflamed?" and into "Is the patient's immune system calibrated correctly?"
| Marker | Category | What it does | What the research shows |
|---|---|---|---|
| CRP | Inflammation | Rises when the body is inflamed | The most-used marker in depression research; inconsistent as a predictor of treatment response |
| IL-6 | Inflammation | Pro-inflammatory signal that triggers CRP | Most consistently elevated marker in depression; mixed results predicting ketamine response |
| TNF-alpha | Inflammation | Launches and sustains inflammation | A drop shortly after infusion tracked with symptom improvement in one ketamine trial |
| IL-8 | Inflammation | Recruits neutrophils to inflamed tissue | Linked to ketamine response in men only; not replicated broadly |
| IL-15 | Immune regulation | Maintains natural killer cells and memory T cells | Ketamine responders started lower than non-responders; normalized after they improved |
| IL-7 | Immune regulation | Keeps B cells and developing T cells alive | Blood levels lined up with gamma activity on brain scans; the relationship reversed after ketamine |
| MCP-1 | Immune regulation | Calls monocytes out of the blood and into tissue | A high MCP-1 to IL-7 ratio predicted non-response to ketamine |
| B-cell signaling | Immune regulation | Antibody production and long-term immune memory | Higher at baseline in responders; reversed after treatment |
Why the B cell finding in this ketamine depression study differs from previous neuroinflammation research
Previous neuroimmune research in psychiatry focused on microglia, the brain's cleanup cells, and monocytes, first responders in the blood. Both belong to the innate immune system, the fast and non-specific arm.
This study found the signal in B cells, part of the adaptive immune system. B cells make antibodies and carry long-term immune memory. Almost nobody was looking there for rapid antidepressant response.
Can a blood test predict who responds to ketamine for treatment-resistant depression?
Possibly, eventually. Previous candidate predictors including IL-6, IL-8, and baseline monocyte count each looked promising and then failed to replicate.
Here, ratios within the IL-7 and IL-15 system predicted both response and non-response in statistical modeling. That is real signal, not a validated test. No clinic can currently order a panel that tells you whether ketamine will work for you.
What this new ketamine and immune marker research means for patients right now
Nothing here changes how ketamine is prescribed today. There is no panel to order and no number that tells you in advance whether an infusion will work for you.
What has changed is the shape of the question: beyond inflammation, there is now evidence that a mis-set immune system plays a role of its own. The CRP and IL-6 findings still hold, and plenty of people with depression do have measurable inflammation driving their symptoms.
This adds a second mechanism alongside that one, and it can be present in a body showing no signs of inflammation at all. It may account for the patients whose labs keep coming back clean while their symptoms do not budge.
If IL-7 and IL-15 hold up in larger studies, the practical gain is knowing before treatment instead of after. For someone who has already cycled through three or four failed antidepressants, that is a difference measured in months and in how many rounds of trial and error they have to sit through.
Curious about ketamine treatment for chronic pain or treatment-resistant depression? Contact our office today.
This article is for educational purposes and is not medical advice. Talk with your physician before starting, stopping, or combining any pain treatment.