Nikhil Prasad Fact checked by:Thailand Medical News Team Apr 25, 2025 4 hours, 11 minutes ago
Medical News: A groundbreaking new study by researchers from the University Hospital Regensburg and several other German institutions has revealed a key mechanism behind the prolonged and debilitating symptoms of Long COVID. The team has identified that patients suffering from the condition display an unusual and persistent overreaction in their immune systems, particularly involving a specific type of immune cell known as CD8+ T cells.
Hyperactivated Killer T Cells and IL-3 Found to Be Driving Long COVID Symptoms
These cells, often referred to as "killer T cells," are essential for eliminating virus-infected cells. However, in Long COVID patients, they appear to remain abnormally activated for months, even up to a year and a half after initial infection. This
Medical News report highlights that such persistent immune activation could be a major contributor to the fatigue, cognitive issues, chest pain, and other symptoms experienced by those living with Long COVID.
Key Immune System Disturbance in Long COVID
The study involved 68 patients with Long COVID, 23 individuals who recovered from COVID-19 without lingering symptoms, and 69 people with no history of SARS-CoV-2 infection. Patients were evaluated for symptoms, immune cell behavior, and the severity of Long COVID using a grading scale.
The standout finding was the elevated activity of CD8+ T cells in Long COVID sufferers. Compared to control groups, these T cells had a sevenfold higher expression of the activation marker CD25. They also showed a twofold increase in memory-type T cells—cells that "remember" past infections and respond rapidly to threats. These shifts suggest a hyperalert immune system stuck in overdrive.
Following stimulation with a general T cell activator, CD8+ T cells from Long COVID patients showed significantly more reactivity. Most notably, these cells released large quantities of a signaling molecule called interleukin-3 (IL-3)—seven times more than in non-Long COVID individuals. IL-3 is a cytokine known to fuel inflammation and has been implicated in autoimmune diseases and chronic fatigue-like conditions.
IL3 and Memory T Cells Strongly Linked to Symptoms
Through additional laboratory tests, the researchers pinpointed that IL-3 production was mainly coming from a subset of CD8+ T cells known as effector-memory and terminal-effector-memory cells. These are cells designed for fast response, but in Long COVID, they appear to be stuck in a hyperactive mode.
Interestingly, IL-3 levels correlated strongly with how severe a patient’s Long COVID symptoms were. Patients with the most disabling symptoms had the highest numbers of IL-3-producing CD8+ cells. These findings suggest that IL-3 could potentially serve as both a biomarker for Long COVID severity and a target for future treatments.
What’s even more concerning is that these immune abnormalities didn’t fade over time. The study tracked patients for more than 18 months after their in
itial infection and found that CD8+ T cells remained highly activated. In some patients, the amount of memory T cells and IL-3 actually increased with time, suggesting a lack of proper immune shutdown.
The Research Institutions Behind the Study
This comprehensive investigation was carried out by scientists from the University Hospital Regensburg’s Department of Nephrology, the Klinik Donaustauf (Departments of Pneumology and Psychosomatic Medicine), the Department of Transplant and Infection Immunology at Saarland University, the Center for Gender-specific Biology and Medicine at Saarland University, the Institute of Clinical Microbiology and Hygiene at the University of Regensburg, and the Leibniz Institute for Immunotherapy.
Potential Treatment Implications
The researchers suggest that targeting this runaway immune response could offer relief for patients. Drugs that suppress overactive T cells—such as low-dose rapamycin or intravenous immunoglobulin—are already being tested in clinical trials. The fact that IL-3 is so prominently involved also raises the possibility of developing IL-3-specific therapies.
Conclusion
The findings of this study offer compelling evidence that Long COVID is not just a psychological or vague condition but is rooted in measurable immune dysfunction—particularly involving CD8+ T cells and IL-3. The data reveals that these immune cells remain in a state of prolonged hyperactivation, contributing to inflammation, fatigue, and cognitive disturbances experienced by many sufferers. Importantly, this persistent immune dysfunction was found to last over 18 months in some cases, underscoring the chronic nature of the syndrome. By identifying IL-3 as a potential key player, researchers have opened the door to more targeted treatment strategies that could finally bring relief to Long COVID patients.
The study findings were published in the peer reviewed journal: Clinical Immunology.
https://www.sciencedirect.com/science/article/pii/S1521661625000774
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Medical News.
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