Category: Biomarker

Plasma Extracellular Vesicle Surface Marker Profiling Reveals Immune Cell-Associated Mitochondrial Membrane Potential Alterations in Long COVID and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Abstract:

Background: Long COVID (LC) is characterized by symptoms persisting at least 3 months after SARS-CoV-2 infection and affecting multiple organ systems. Diagnosis relies on subjective criteria without established biomarkers. Immune dysregulation and mitochondrial dysfunction are implicated in LC pathophysiology. Given clinical overlap with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), we investigated whether plasma extracellular vesicles (EVs) capture shared molecular signatures.

Methods: Plasma EVs from 125 individuals across pandemic-era and prepandemic cohorts were analyzed. The pandemic-era cohort included COVID-Recovered, LC with ME/CFS phenotype (LC-ME/CFS), and ME/CFS without infection (pan-ME/CFS). The prepandemic cohort included ME/CFS and matched controls. Extracellular vesicles were isolated using size-exclusion chromatography. Concentration and size were assessed by nanoparticle tracking analysis, and surface markers and mitochondrial membrane potential were evaluated by flow cytometry.

Results: Both pan-ME/CFS and LC-ME/CFS exhibited elevated EV concentrations compared with COVID-recovered controls after false discovery rate (FDR) correction (q = 0.0042 and 0.0024). Leukocyte-, monocyte/macrophage-, and platelet-derived EVs were increased, whereas B cell-derived EVs were reduced in both groups. Compared with controls, pan-ME/CFS demonstrated increased mitochondrial membrane potential in B cell-, monocyte/macrophage-, and NK cell-derived subsets after FDR correction, whereas no significant differences were observed in LC-ME/CFS. Prepandemic ME/CFS showed a nominal increase in leukocyte-derived EVs that did not persist after correction, whereas elevated mitochondrial membrane potential in B cell-derived EV subsets remained significant.

Conclusions: ME/CFS and LC-ME/CFS demonstrate partially overlapping immune cell-associated EV alterations. Mitochondrial membrane potential alterations within selected immune-derived EV subsets, particularly B cell-associated EVs, suggest immune-metabolic involvement. Plasma EV profiling may inform future biomarker development.

Source: Ikeda G, Koike-Ieki M, Inoue H, Dadhania AV, El Kamari V, Jagannathan P, Geng LN, Miglis MG, Shafer RW, Yang PC, Bonilla HF. Plasma Extracellular Vesicle Surface Marker Profiling Reveals Immune Cell-Associated Mitochondrial Membrane Potential Alterations in Long COVID and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Open Forum Infect Dis. 2026 May 12;13(5):ofag209. doi: 10.1093/ofid/ofag209. PMID: 42131622; PMCID: PMC13166156. https://pmc.ncbi.nlm.nih.gov/articles/PMC13166156/ (Full text)

Involvement of autoantibodies against G protein-coupled receptors in post-COVID condition and Chronic Fatigue Syndrome

Abstract:

Post-COVID condition (PCC) and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) are chronic disorders marked by fatigue, autonomic dysfunction, and cognitive impairment. Autoantibodies (AAbs) targeting adrenergic and muscarinic receptors have been implicated in their pathophysiology. This study aimed to investigate the association between these AAbs, autonomic nervous system (ANS) function, and cognitive performance in PCC and ME/CFS.

We included 96 PCC patients, 59 ME/CFS patients, and 36 healthy controls (HCs). Plasma AAbs against α1, β1, β2 adrenergic and M1-M4 muscarinic receptors were measured via ELISA. ANS function was evaluated using COMPASS-31, Sudoscan, hemodynamic tests (deep breathing, Valsalva, tilt test), and heart rate variability. Cognitive domains assessed included attention, fluency, processing speed, memory, visuoconstruction, perception, and executive functions.

ME/CFS patients had significantly higher β2 adrenergic AAb titers than PCC and HCs (F₂,₁₈₆ = 3.15, p = 0.046). PCC patients showed more borderline/pathological M3 muscarinic AAb results compared to HCs. β2 AAb levels correlated with increased autonomic symptoms in PCC (r = 0.27, p = 0.048) and sympathovagal imbalance in ME/CFS (r = 0.45, p = 0.001). In ME/CFS, M1, M3, and M4 AAb titers positively correlated with verbal and working memory performance.

Distinct AAb profiles in PCC and ME/CFS suggest potential differences in immunological mechanisms. β2 adrenergic receptor AAbs were associated with measures of autonomic dysfunction in PCC patients, and with sympathovagal parameters in ME/CFS patients. Muscarinic AAbs were correlated with cognitive performance in ME/CFS, supporting a potential role of these autoantibodies in autonomic and cognitive dysfunction. These findings support further investigation of AAbs as biomarkers and therapeutic targets.

Source: Azcue N, Prada A, Del Pino R, Acera M, Fernández-Valle T, Ayo-Mentxakatorre N, Pérez-Concha T, Murueta-Goyena A, Lafuente JV, López de Munain A, Ruiz Irastorza G, Ribacoba L, Gabilondo I, Tijero-Merino B, Gómez-Esteban JC. Involvement of autoantibodies against G protein-coupled receptors in post-COVID condition and Chronic Fatigue Syndrome. Sci Rep. 2026 May 5. doi: 10.1038/s41598-026-49131-9. Epub ahead of print. PMID: 42082542. https://www.nature.com/articles/s41598-026-49131-9 (Full text available as PDF file)

A hypothesis connecting dysgeusia due to defects in ATP-P2X3 signaling and fatigue in myalgic encephalomyelitis/chronic fatigue syndrome: lessons learned from long-COVID

Abstract:

Myalgic encephalomyelitis (ME)/chronic fatigue syndrome (CFS) is a neuroimmune disease characterized by debilitating post-exertional malaise (PEM), brain-fog/cognitive problems, and dysregulation of the autonomic nervous system. Currently, there are no objective biomarkers for ME/CFS despite decades of research.

Here, we compile evidence from literature that supports taste dysfunction, particularly alterations of taste perception mediated by Type II taste receptor cells, may be a critical underrecognized feature of ME/CFS. The impetus is drawn from the emerging evidence of clinicopathological similarities between long-COVID and ME/CFS. We discuss in parallel the mechanisms of cellular metabolism, inflammation, vascular dysfunction, and autonomic dysregulation in ME/CFS and long-COVID pathophysiology.

We postulate that mechanistically, dysregulation of ATP signaling through P2X2/P2X3 purinergic receptors underlies both gustatory impairment and core ME/CFS symptoms. Adopting information from the NIH-RECOVER shared resources, we present evidence that suggests chemosensory dysfunction as a potential indicator of progression/severity of PEM. We discuss standardized taste testing as a non-invasive screening tool complementary to molecular biomarkers for ME/CFS.

Notwithstanding, we acknowledge the limitations, confounding and contributing factors such as medications and deficiencies that may exacerbate or independently cause taste-related symptoms in ME/CFS.

In conclusion, we present a compelling case for the multi-factorial role of taste dysfunction in ME/CFS and suggest specific research priorities for investigating the relationship between chemosensory function and post-viral chronic illness.

Source: Srinivasan M, Joseph PV. A hypothesis connecting dysgeusia due to defects in ATP-P2X3 signaling and fatigue in myalgic encephalomyelitis/chronic fatigue syndrome: lessons learned from long-COVID. Front Med (Lausanne). 2026 Apr 8;13:1808646. doi: 10.3389/fmed.2026.1808646. PMID: 42040552; PMCID: PMC13107777. https://pmc.ncbi.nlm.nih.gov/articles/PMC13107777/ (Full text)

Proteomic signatures in cerebrospinal fluid and their clinical associations in patients with ME/CFS

Abstract:

This study evaluated the cerebrospinal fluid (CSF) proteomes from 31 patients diagnosed with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). We quantified 902 proteins, each expressed in at least eleven samples, and systematically categorized clinical factors relevant to ME/CFS symptoms-including autonomic dysfunction, neuroinflammation and metabolic disturbances.

Differentially expressed protein and pathway analyses evaluated protein features associated with both postural orthostatic tachycardia syndrome (POTS) status and disease severity among the patients, while ratio-based analysis further explored associations with severity ratings.

Data are available via ProteomeXchange with identifier PXD076216. Neutrophil degranulation and platelet activation were enriched in patients with POTS, and several pathways, such as the complement cascade, coagulation-related pathways and IGFBP‑mediated insulin-like growth factor transport, were enriched in severe cases. Ratio-based analysis identified four biologically interpretable severity-associated protein ratios related to cellular stress, extracellular remodelling and immune-neuronal interaction.

Together, these findings provide insight into the biological processes associated with clinical heterogeneity in ME/CFS and generate hypotheses for future validation in larger independent cohorts.

Source: Bragée B, Li P, Meadows D, Widgren A, Sjögren P, Ghatan PH, Bertilson BC, Xiao W, Bergquist J. Proteomic signatures in cerebrospinal fluid and their clinical associations in patients with ME/CFS. Sci Rep. 2026 Apr 3. doi: 10.1038/s41598-026-46965-1. Epub ahead of print. PMID: 41932997.  https://www.nature.com/articles/s41598-026-46965-1 (Full text available as PDF file)

Authors’ Response to “Comment on ‘SMPDL3B as a novel biomarker and therapeutic target in myalgic encephalomyelitis’”

Letter:

We thank Chen and Yan for their thoughtful and positive comments on our recent publication and for their interest in the translational implications of SMPDL3B biology in myalgic encephalomyelitis (ME) [, ]. Their letter provides a welcome opportunity to clarify methodological points related to biomarker validation, in vitro pharmacological assays, and mechanistic interpretation []. We appreciate this constructive dialogue and address each issue below in a collegial and scientifically grounded manner.

Read the rest of this letter HERE>>

Source: Rostami-Afshari B, Elremaly W, Franco A, Moreau A. Authors’ Response to “Comment on ‘SMPDL3B as a novel biomarker and therapeutic target in myalgic encephalomyelitis'”. J Transl Med. 2026 Jan 16;24(1):75. doi: 10.1186/s12967-025-07583-z. PMID: 41546078; PMCID: PMC12809929. https://pmc.ncbi.nlm.nih.gov/articles/PMC12809929/ (Full text)

People with ME/CFS have a consistent faulty cellular structure, new research confirms

Press Release:

A faulty ion channel function is a consistent biological feature of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), providing long-awaited validation for hundreds of thousands of Australians living with the debilitating illness.

The new Griffith University research found a crucial cellular structure responsible for calcium transport, the TRPM3 ion channel, was faulty in immune cells from people with ME/CFS.

The paper “Large-scale investigation confirms TRPM3 ion channel dysfunction in ME/CFS” has been published in Frontiers in Medicine.

Director and senior author, Professor Sonya Marshall-Gradisnik from Griffith’s National Center for Neuroimmunology and Emerging Diseases (NCNED), said the TRPM3 played an essential role in calcium transport into cells, regulating responses properly in the body, immune function, and maintaining normal cellular balance.

“When it fails, cells cannot function properly as calcium signaling is essential for healthy immune cell activity,” Professor Marshall-Gradisnik said.

“Our findings provide clear and definitive scientific evidence that TRPM3 ion channels are not working properly in people with ME/CFS.”

Read the rest of this press release HERE>>

Large-scale investigation confirms TRPM3 ion channel dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Abstract:

Introduction: Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a chronic disease hallmarked by multiple systemic symptoms, such as neurocognitive, respiratory, immunological, gastrointestinal, and cardiovascular impairment, which worsen following physical and mental exertion. ME/CFS is characterized by an elusive pathomechanism, profound impact on quality of life, and an absence of diagnostic tests or evidence-based treatments. Transient Receptor Potential Melastatin 3 (TRPM3) ion channel has been suggested as a potential biomarker and target for therapeutics in people with ME/CFS, supported by a series of publications reporting genetic and protein changes. This study aimed to undertake a multi-site, large-scale investigation to determine the consistency of TRPM3 ion channel dysfunction in people with ME/CFS.

Methods: TRPM3 ion channel activity was assessed in two distinct laboratory sites by independent investigators using whole-cell patch-clamp recordings performed in isolated natural killer (NK) cells from 36 ME/CFS participants, characterized according to the Canadian Consensus Criteria, and 42 healthy controls. The Mann–Whitney U test was used to compare endogenous TRPM3-like currents between cohorts. The effect of location was determined using a covariance analysis, while antagonist sensitivity was determined using Fisher’s Exact test.

Results: Electrophysiological experiments revealed a significant reduction in TRPM3 function in NK cells from individuals diagnosed with ME/CFS compared with controls in all parameters analyzed. Importantly, there was no significant effect of the laboratory sites on the results of this investigation, which confirms TRPM3 as a consistent biomarker for ME/CFS.

Conclusion: The current large-sample-size study confirmed previous results regarding TRPM3 ion channel dysfunction in NK cells in ME/CFS, demonstrating involvement of TRPM3 in the pathomechanism of this condition. Therefore, this multiple-site investigation offers strong evidence demonstrating TRPM3 as a potential biomarker for the diagnosis of ME/CFS, given the accumulating evidence.

Source: Sasso Etianne Martini , Er Teagan S. , Eaton-Fitch Natalie , Hool Livia , Muraki Katsuhiko , Marshall-Gradisnik Sonya. Large-scale investigation confirms TRPM3 ion channel dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Frontiers in Medicine, Volume 12 – 2026. https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2025.1703924 10.3389/fmed.2025.1703924 ISSN=2296-858X https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2025.1703924/full (Full text)

Wheat and chaff in Myalgic Encephalomyelitis/Chronic fatigue syndrome (ME/CFS) in clinics and laboratory

To the Editor,

We read the contribution by Hunter et al., titled “Development and validation of blood-based diagnostic biomarkers for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) using EpiSwitch® 3-dimensional genomic regulatory immuno-genetic profiling” in this journal, initially impressed for the large collection of data. They actually presented a novel, genome-wide epigenetic profiling approach using EpiSwitch® technology to identify potential diagnostic biomarkers for ME/CFS [1]. The use of 3D chromatin conformation signatures provides a fresh perspective on disease-specific gene regulation, moving beyond conventional transcriptomics and methylation analyses. In general, the diagnostic model demonstrates impressive sensitivity (92%) and specificity (98%) in distinguishing ME/CFS patients from controls, suggesting real clinical potential [1]. Moreover, the application of advanced machine learning techniques adds analytical robustness, while pathway analysis identifies biologically plausible immune-related mechanisms. This integrative approach sets a promising foundation for future biomarker-driven diagnostics and personalized therapy stratification in ME/CFS. Fundamentally, they presented a retrospective case-control analysis aiming to identify diagnostic epigenetic markers for ME/CFS using 3D chromatin conformation profiling (EpiSwitch®). However, while the authors make bold claims regarding diagnostic sensitivity and specificity, the paper suffers from multiple scientific weaknesses and methodological ambiguities that undermine its validity and translational relevance.

First, the article repeatedly asserts that “immune dysregulation” is a hallmark of ME/CFS, citing elevated pro-inflammatory cytokines and natural killer (NK) cell dysfunction. However, whereas the authors cite updated papers with a presumptive relationship with the issue, a critical omission here is the lack of citation of early foundational immunological studies in ME/CFS [2]. Notably absent is the 1994 work by Tirelli et al. in the Scandinavian Journal of Immunology, which documented, for the first time, immunological abnormalities in CFS patients and could serve as an important historical anchor for claims of immune dysregulation [2]. This omission raises concerns about reporting bias and selective citation to frame the narrative around newer, possibly more aligned findings with the current study methodology [2, 3].

Additionally, the paper refers to “ME/CFS inclusion criteria” as requiring severe CFS with patients being “housebound,” but fails to specify which diagnostic criteria were used, whether the Fukuda, Canadian Consensus, International Consensus, or IOM/NAM criteria [1]. This lack of precision is critical, as different case definitions yield different cohorts in terms of clinical features and biological signatures. Using “severe housebound” as a criterion, without reference to a validated clinical definition or stratification tool (e.g., Bell Disability Scale), introduces subjectivity and undermines the reproducibility of patient selection. The term “housebound” is not a recognized diagnostic stratifier and suggests imprecise cohort construction.

Further ambiguity arises when the authors discuss the control group. They state that controls had “none of the four key CFS symptoms present or in the past” and “preferably an existing history of glandular fever or COVID.” The phrase “preferably” is ambiguous and methodologically problematic [1]. Did the control group actually include individuals with prior infectious mononucleosis or COVID-19, and if so, how were these illnesses verified? The phrase “preferably” suggests either inconsistency in selection or retrospective rationalization, both of which compromise the clarity and control of variables in the study. Furthermore, it is scientifically incoherent to describe individuals as controls (i.e., free from ME/CFS) while also including those with a known post-infectious risk profile, potentially biasing the control group with latent post-viral immunogenetic changes [1].

There is further conceptual confusion when the authors state that the ME/CFS network reveals some overlap with pathways involved in multiple sclerosis (MS) and rheumatoid arthritis (RA). While such overlaps are plausible and worth exploring, the authors do not sufficiently explain the biological rationale for this claim or its relevance to ME/CFS pathophysiology [1]. They reference IL-2, IL-10, CD4, and TLR pathways as shared elements, but these are highly pleiotropic and non-specific immunological signals.

The mere presence of these markers in ME/CFS does not imply mechanistic similarity to MS or RA. Without longitudinal or functional studies, this comparison becomes speculative and possibly misleading, especially given the known heterogeneity of ME/CFS and the distinct immunopathology of autoimmune diseases like MS.

Read the rest of this letter HERE.

Source: Tirelli U, Franzini M, Chirumbolo S. Wheat and chaff in Myalgic Encephalomyelitis/Chronic fatigue syndrome (ME/CFS) in clinics and laboratory. J Transl Med. 2026 Jan 5;24(1):20. doi: 10.1186/s12967-025-07397-z. PMID: 41491817. https://link.springer.com/article/10.1186/s12967-025-07397-z (Full text)

Exploring a genetic basis for the metabolic perturbations in ME/CFS using UK Biobank

Highlights:

  • ME/CFS shows distinct genetic influences on metabolic regulation.
  • Lipid and hormone-related pathways emerge as key areas of interest.
  • Many small genetic effects may collectively disrupt metabolic resilience in ME/CFS.

Summary:

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a clinically heterogeneous disease lacking approved therapies. To assess genetic susceptibility towards a specific metabolic phenotype, we performed a genome-wide association study on plasma biomarker levels (mGWAS) in ME/CFS patients (n=875) and healthy controls (HCs) (n=36,033).
We identified 112 significant SNP–biomarker associations in ME/CFS, compared with 4,114 in HCs. Two SNPs specific to ME/CFS, mapping to HSD11B1 and SCGN, were associated to phospholipids in extra-large very low-density lipoproteins (VLDL) and total fatty acids respectively. Genetic effects of VLDL associations were among the least correlated between ME/CFS and HCs. Heterogeneity tests found differential effects for several lipid traits at ADAP1, NR1H3 and CD40, which are involved in immune regulation.
ME/CFS mGWAS summary statistics were decomposed to uncover shared genetic-metabolic patterns, where enrichment analysis highlighted pathways in lipid metabolism, neurotransmitter transport, and inflammation. These findings provide a genetic and molecular rationale for patient heterogeneity and suggest a polygenic predisposition in which many small-effect variants may jointly perturb metabolic mechanisms.
Source: Katherine Huang, Muhammad Muneeb, Natalie Thomas, Elena K. Schneider-Futschik, Paul R. Gooley, David B. Ascher, Christopher W. Armstrong. Exploring a genetic basis for the metabolic perturbations in ME/CFS using UK Biobank. iScience, 2025, 114316 ISSN 2589-0042, https://doi.org/10.1016/j.isci.2025.114316. https://www.sciencedirect.com/science/article/pii/S2589004225025775 (Full text available as PDF file)