Researchers Identify First Potential Biomarker for Long COVID Diagnosis
核心洞察
Researchers from TGen (搜索) and Lundquist Institute have identified SARS-CoV-2 (搜索) protein fragments in extracellular vesicles (搜索) as a potential biomarker for long COVID (搜索), offering the first specific diagnostic indicator for the condition.
The study analyzed blood samples from 14 long COVID (搜索) patients and found 65 distinct viral protein fragments from the virus's Pp1ab protein (搜索) within extracellular vesicles (搜索), which were not detected in pre-pandemic control samples.
While promising, the biomarker showed subtle molecular signals that were not consistently detected at every blood collection time point, requiring further validation studies to determine clinical utility.
Researchers from the Translational Genomics Research Institute (TGen (搜索)) and the Lundquist Institute for Biomedical Innovation (搜索) at Harbor-UCLA Medical Center have identified a potential biomarker for long COVID (搜索) that could revolutionize diagnosis of the condition. The discovery, published in the journal Infection, represents the first specific and quantifiable indicator for confirming long COVID, addressing a critical gap in clinical practice.
Currently, clinicians diagnose long COVID (搜索) based solely on a collection of symptoms that patients develop after SARS-CoV-2 (搜索) infection, without any confirmatory laboratory tests. "If a patient arrives in clinic and they relate the persistence of typical signs and symptoms of long COVID, 12 weeks or more after COVID-19 (搜索) infection, I give them a presumptive diagnosis, but I don't have any blood tests or biomarkers to confirm this diagnosis," said William Stringer, M.D., a Lundquist Institute investigator and senior author on the study.
Detection of Viral Fragments in Blood
The research team detected SARS-CoV-2 (搜索) protein fragments within extracellular vesicles (搜索) (EVs) – tiny, naturally occurring packages that help cells share proteins, metabolites, and other materials. The researchers collected and analyzed blood samples from 14 patients over 12 weeks of aerobic exercise training, totaling 56 samples in a clinical trial on long COVID (搜索).
The analysis revealed 65 distinct protein fragments from SARS-CoV-2 (搜索) inside the EVs. These fragments originate from the virus's Pp1ab protein (搜索), an RNA Replicase (搜索) enzyme crucial to how the virus copies itself and produces other viral particles. This protein is found uniquely in SARS-CoV-2 and not in uninfected human cells, noted Asghar Abbasi, Ph.D., a Lundquist Institute investigator and first author of the study.
Significant Findings and Limitations
The researchers found that viral peptides were demonstrated in each subject, though not in each blood draw, in the EVs of long COVID (搜索) patients. Importantly, these fragments were not detected in a separate control group of pre-pandemic EV samples, providing specificity for the biomarker.
However, the molecular signal showed limitations. "While promising, the molecular signal of the viral peptides within the study samples was observed to be subtle and not consistently detected at every blood collection time point," said Patrick Pirrotte, Ph.D., associate professor at TGen (搜索) and co-senior author of the study. "There's still a lot to unpack that we don't know at this point."
Implications for Viral Persistence
The findings contribute to growing evidence suggesting that SARS-CoV-2 (搜索) may persist in certain body tissues long after initial infection. Some researchers hypothesize these lingering viral reservoirs could play a role in long COVID (搜索) development. The mechanism by which the virus reaches tissues without its usual entry points, such as the brain, remains unclear and may be related to EV particles.
"We thought that maybe if the virus is circulating or moving in the body, we should try to see if EVs are carrying those viral fragments," Abbasi explained. This hypothesis became part of an ongoing clinical trial studying EVs and their potential links to changes in immune function related to exercise and post-exertional malaise (搜索), a common symptom in long COVID (搜索) patients.
Unanswered Questions
Despite the promising findings, several mechanistic questions remain unresolved. Although the identified peptides originated from one of the virus's largest proteins, researchers did not detect other comparably large proteins indicative of active viral replication. The peptides contained in the EVs may represent molecular "trash" left over after the formation of new viral proteins rather than evidence of ongoing replication.
"We haven't run [our tests] on people without long COVID (搜索) symptoms who are currently, or who were, infected with COVID," said Stringer. "This raises the question: is this just continuing to take out the trash from the COVID infected cell or is this really ongoing replication someplace? I think that's the mechanistic issue that needs to be resolved in future studies."
The researchers acknowledge that additional validation studies are needed to confirm whether exercise itself drives viral protein expression or if there exists a permanent viral reservoir in cells that can be detected at specific time points. Future research will need to test the biomarker in broader patient populations, including those without long COVID (搜索) symptoms who have been infected with COVID-19 (搜索), to establish its clinical utility and diagnostic accuracy.