Tag: CD4

Immune cell exhaustion, dysfunction, and metabolism in myalgic encephalomyelitis/chronic fatigue syndrome

Abstract;
Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a chronic and incapacitating multisystem condition with unknown etiology, no cure, and no FDA- approved treatments, all of which can be attributed to historical underfunding, widespread misinformation, and the complexity of the disease. Many patients encounter several immune-related symptoms, extreme fatigue, post-exertional malaise, and a flu-like onset. Studies have documented changes in ME/CFS immune cell populations and decreased natural killer (NK) cell performance, along with aberrant cytokine production, reduced glycolysis in T cells, and altered metabolites relevant to fatty acid oxidation, implicating potential intracellular metabolic dysregulation.
This knowledge prompted me to investigate fatty acid oxidation and immune cell functional states in isolated ME/CFS lymphocytes. Using extracellular flux analysis and flow cytometry, I observed elevated fatty acid oxidation levels in ME/CFS immune cells, including NK cells, CD4+ memory cells, CD4+ effector cells, CD8+ naïve cells, and CD8+ memory cells compared to healthy controls, particularly during high energy demands and activation. My findings suggest a metabolic dysfunction in ME/CFS immune cells, consistent with T cell exhaustion – a state that hinders immune cell proliferation, survival, and cytokine production following persistent antigen stimulation.
Building upon these results, I further investigated immune cell exhaustion and dysfunction in isolated CD8+ and CD4+ T cells from ME/CFS and healthy samples. I analyzed T cell sub-populations, including naïve, effector, memory, regulatory, and helper T cells, for frequencies of inhibitory receptors and transcription factors associated with dysfunctional immune cell states.
I detected distinct transcription factor dynamics and elevated exhausted T cell phenotype proportions in ME/CFS CD8+ T cell populations compared to healthy controls. In ME/CFS CD4+ T cells, I also observed altered inhibitory receptor population frequencies compared to healthy control samples. Moreover, dysfunctional T cell features correlated with ME/CFS health status and symptom presentation.
Overall, my findings detect dysfunctional T cell states in specific ME/CFS cell populations, which can lead to reduced effector function that may contribute to ME/CFS symptom presentation. This work highlights the significance of assessing both metabolic components and immune cell dysfunction-associated targets in the development of potential therapeutic interventions for individuals with ME/CFS.
Source: Maya, Jessica. Immune cell exhaustion, dysfunction, and metabolism in myalgic encephalomyelitis/chronic fatigue syndrome. Cornell Theses and Dissertations. 2024. https://ecommons.cornell.edu/items/242f8723-6f87-47cc-b36d-bf51a21f4255

Blood T cell phenotypes correlate with fatigue severity in post-acute sequelae of COVID-19

Abstract:

Purpose: Post-acute sequelae of COVID-19 (PASC) affect approximately 10% of convalescent patients. The spectrum of symptoms is broad and heterogeneous with fatigue being the most often reported sequela. Easily accessible blood biomarkers to determine PASC severity are lacking. Thus, our study aimed to correlate immune phenotypes with PASC across the severity spectrum of COVID-19.

Methods: A total of 176 originally immunonaïve, convalescent COVID-19 patients from a prospective cohort during the first pandemic phase were stratified by initial disease severity and underwent clinical, psychosocial, and immune phenotyping around 10 weeks after first COVID-19 symptoms. COVID-19-associated fatigue dynamics were assessed and related to clinical and immune phenotypes.

Results: Fatigue and severe fatigue were commonly reported irrespective of initial COVID-19 severity or organ-specific PASC. A clinically relevant increase in fatigue severity after COVID-19 was detected in all groups. Neutralizing antibody titers were higher in patients with severe acute disease, but no association was found between antibody titers and PASC. While absolute peripheral blood immune cell counts in originally immunonaïve PASC patients did not differ from unexposed controls, peripheral CD3+CD4+ T cell counts were independently correlated with fatigue severity across all strata in multivariable analysis.

Conclusions: Patients were at similar risk of self-reported PASC irrespective of initial disease severity. The independent correlation between fatigue severity and blood T cell phenotypes indicates a possible role of CD4+ T cells in the pathogenesis of post-COVID-19 fatigue, which might serve as a blood biomarker.

Source: Pink, I., Hennigs, J.K., Ruhl, L. et al. Blood T cell phenotypes correlate with fatigue severity in post-acute sequelae of COVID-19. Infection (2023). https://doi.org/10.1007/s15010-023-02114-8 https://link.springer.com/article/10.1007/s15010-023-02114-8 (Full text)

Cytometry profiling of ex vivo recall responses to Coxiella burnetii in previously naturally exposed individuals reveals long-term changes in both adaptive and innate immune cellular compartments

Abstract:

Introduction: Q fever, caused by the intracellular bacterium Coxiella burnetii, is considered an occupational and biodefense hazard and can result in debilitating long-term complications. While natural infection and vaccination induce humoral and cellular immune responses, the exact nature of cellular immune responses to C. burnetii is incompletely understood. The current study seeks to investigate more deeply the nature of long-term cellular recall responses in naturally exposed individuals by both cytokine release assessment and cytometry profiling.

Methods: Individuals exposed during the 2007-2010 Dutch Q fever outbreak were grouped in 2015, based on a C. burnetii-specific IFNγ release assay (IGRA), serological status, and self-reported clinical symptoms during initial infection, into asymptomatic IGRA-negative/seronegative controls, and three IGRA-positive groups (seronegative/asymptomatic; seropositive/asymptomatic and seropositive/symptomatic). Recall responses following in vitro re-stimulation with heat-inactivated C. burnetii in whole blood, were assessed in 2016/2017 by cytokine release assays (n=55) and flow cytometry (n=36), and in blood mononuclear cells by mass cytometry (n=36).

Results: Cytokine release analysis showed significantly elevated IL-2 responses in all seropositive individuals and elevated IL-1β responses in those recovered from symptomatic infection. Comparative flow cytometry analysis revealed significantly increased IFNγ, TNFα and IL-2 recall responses by CD4 T cells and higher IL-6 production by monocytes from symptomatic, IGRA-positive/seropositive individuals compared to controls. Mass cytometry profiling and unsupervised clustering analysis confirmed recall responses in seropositive individuals by two activated CD4 T cell subsets, one characterized by a strong Th1 cytokine profile (IFNγ+IL-2+TNFα+), and identified C. burnetii-specific activation of CD8 T cells in all IGRA-positive groups. Remarkably, increased C. burnetii-specific responses in IGRA-positive individuals were also observed in three innate cell subpopulations: one characterized by an IFNγ+IL-2+TNFα+ Th1 cytokine profile and lack of canonical marker expression, and two IL-1β-, IL-6- and IL-8-producing CD14+ monocyte subsets that could be the drivers of elevated secretion of innate cytokines in pre-exposed individuals.

Discussion: These data highlight that there are long-term increased responses to C. burnetii in both adaptive and innate cellular compartments, the latter being indicative of trained immunity. These findings warrant future studies into the protective role of these innate responses and may inform future Q fever vaccine design.

Source: Raju Paul S, Scholzen A, Reeves PM, Shepard R, Hess JM, Dzeng RK, Korek S, Garritsen A, Poznansky MC, Sluder AE. Cytometry profiling of ex vivo recall responses to Coxiella burnetii in previously naturally exposed individuals reveals long-term changes in both adaptive and innate immune cellular compartments. Front Immunol. 2023 Oct 11;14:1249581. doi: 10.3389/fimmu.2023.1249581. PMID: 37885896; PMCID: PMC10598782. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10598782/ (Full text)

Increased SARS-CoV-2 reactive low avidity T cells producing inflammatory cytokines in pediatric post-acute COVID-19 sequelae (PASC)

Abstract:

Background: A proportion of the convalescent SARS-CoV-2 pediatric population presents nonspecific symptoms, mental health problems and a reduction in quality of life similar to myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and long COVID-19 symptomatic. However, data regarding its clinical manifestation and immune mechanisms are currently scarce.

Methods: In this study, we perform a comprehensive clinical and immunological profiling of 17 convalescent COVID-19 children with post-acute COVID-19 sequelae (PASC) manifestation and 13 convalescent children without PASC manifestation. A detailed medical history, blood and instrumental tests and physical examination were obtained from all patients. SARSCoV-2 reactive T cell response was analyzed via multiparametric flowcytometry and the humoral immunity was addressed via pseudovirus neutralization and ELISA assay.

Results: The most common PASC symptoms were shortness of breath/exercise intolerance, paresthesia, smell/taste disturbance, chest pain, dyspnea, headache and lack of concentration. Blood count and clinical chemistry showed no statistical differences among the study groups. We detected higher frequencies of spike (S) reactive CD4+ and CD8+ T cells among the PASC study group, characterized by TNFα and IFNγ production and low functional avidity. CRP levels are positively correlated with IFNγ producing reactive CD8+ T cells.

Conclusions: Our data might indicate a possible involvement of a persistent cellular inflammatory response triggered by SARS-CoV-2 in the development of the observed sequelae in pediatric PASC. These results may have implications on future therapeutic and prevention strategies.

Source: Krystallenia Paniskaki, et al. Increased SARS-CoV-2 reactive low avidity T cells producing inflammatory cytokines in pediatric post-acute COVID-19 sequelae (PASC) https://d197for5662m48.cloudfront.net/documents/publicationstatus/144335/preprint_pdf/a855de5e766f9457795050e56413075a.pdf (Full text)

Surveying the Metabolic and Dysfunctional Profiles of T Cells and NK Cells in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Abstract:

Millions globally suffer from myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). The inflammatory symptoms, illness onset, recorded outbreak events, and physiological variations provide strong indications that ME/CFS, at least sometimes, has an infectious origin, possibly resulting in a chronic unidentified viral infection.
Meanwhile, studies exposing generalized metabolic disruptions in ME/CFS have stimulated interest in isolated immune cells with an altered metabolic state. As the metabolism dictates the cellular function, dissecting the biomechanics of dysfunctional immune cells in ME/CFS can uncover states such as exhaustion, senescence, or anergy, providing insights into the consequences of these phenotypes in this disease. Despite the similarities that are seen metabolically between ME/CFS and other chronic viral infections that result in an exhausted immune cell state, immune cell exhaustion has not yet been verified in ME/CFS.
This review explores the evidence for immunometabolic dysfunction in ME/CFS T cell and natural killer (NK) cell populations, comparing ME/CFS metabolic and functional features to dysfunctional immune cell states, and positing whether anergy, exhaustion, or senescence could be occurring in distinct immune cell populations in ME/CFS, which is consistent with the hypothesis that ME/CFS is a chronic viral disease.
This comprehensive review of the ME/CFS immunometabolic literature identifies CD8+ T cell exhaustion as a probable contender, underscores the need for further investigation into the dysfunctional state of CD4+ T cells and NK cells, and explores the functional implications of molecular findings in these immune-cell types. Comprehending the cause and impact of ME/CFS immune cell dysfunction is critical to understanding the physiological mechanisms of ME/CFS, and developing effective treatments to alleviate the burden of this disabling condition.
Source: Maya J. Surveying the Metabolic and Dysfunctional Profiles of T Cells and NK Cells in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. International Journal of Molecular Sciences. 2023; 24(15):11937. https://doi.org/10.3390/ijms241511937 https://www.mdpi.com/1422-0067/24/15/11937 (Full text)

Divergent Adaptive Immune Responses Define Two Types Of Long Covid

The role of adaptive immune responses in long COVID remains poorly understood, with contrasting hypotheses suggesting either an insufficient antiviral response or an excessive immune response associated with inflammatory damage. To address this issue, we set to characterize humoral and CD4+ T cell responses in long COVID patients prior to SARS-CoV-2 vaccination.

Long COVID patients who were seropositive (LC+, n=28) or seronegative (LC-, n=23) by spike ELISA assay were recruited based on (i) an initial SARS-CoV-2 infection documented by PCR or the conjunction of three major signs of COVID-19 and (ii) the persistence or resurgence of at least 3 symptoms for over 3 months. They were compared to COVID patients with resolved symptoms (RE, n=29) and uninfected control individuals (HD, n=29).

The spectrum of persistent symptoms proved similar in both long COVID groups, with a trend for a higher number of symptoms in the seronegative group (median=6 vs 4.5; P=0.01). The use a highly sensitive S-flow assay enabled the detection of low levels of SARS-CoV-2 spike-specific IgG in 22.7% of ELISA-seronegative long COVID (LC-) patients. In contrast, spike-specific IgG levels were uniformly high in the LC+ and RE groups.

Multiplexed antibody analyses to 30 different viral antigens showed that LC-patients had defective antibody responses to all SARS-CoV-2 proteins tested but had in most cases preserved responses to other viruses. A sensitive primary T cell line assay revealed low but detectable SARS-CoV-2-specific CD4 responses in 39.1% of LC-patients, while response frequencies were high in the LC+ and RE groups. Correlation analyses showed overall strong associations between humoral and cellular responses, with exceptions in the LC-group.

These findings provide evidence for two major types of antiviral immune responses in long COVID. Seropositive patients showed coordinated cellular and humoral responses at least as high as those of recovered patients. In contrast, ELISA-seronegative long COVID patients showed overall low antiviral responses, with detectable specific CD4+ T cells and/or antibodies in close to half of patients (52.2%). These divergent findings in patients sharing a comparable spectrum of persistent symptoms raise the possibility of multiple etiologies in long COVID.

Source: Jérôme Kervevan, Isabelle Staropoli, Dorsaf Slama, Raphaël Jeger-Madiot, Françoise Donnadieu, Delphine Planas, Marie-Pierre Pietri, Wiem Loghmari-Bouchneb, Motolete A. Tanah, Rémy Robinot, Faroudy Boufassa, Michael White, Dominique SALMON and Lisa A. Chakrabarti. Front. Immunol. Sec. Viral Immunology. Volume 14 – 2023 | doi: 10.3389/fimmu.2023.1221961 https://www.frontiersin.org/articles/10.3389/fimmu.2023.1221961/abstract

Prolonged T-cell activation and long COVID symptoms independently associate with severe COVID-19 at 3 months

Abstract:

COVID-19 causes immune perturbations which may persist long-term, and patients frequently report ongoing symptoms for months after recovery. We assessed immune activation at 3-12 months post hospital admission in 187 samples from 63 patients with mild, moderate or severe disease and investigated whether it associates with long COVID.

At 3 months, patients with severe disease displayed persistent activation of CD4+ and CD8+ T-cells, based on expression of HLA-DR, CD38, Ki67 and granzyme B, and elevated plasma levels of IL-4, IL-7, IL-17 and TNF-α compared to mild and/or moderate patients. Plasma from severe patients at 3 months caused T-cells from healthy donors to upregulate IL-15Rα, suggesting that plasma factors in severe patients may increase T-cell responsiveness to IL-15-driven bystander activation.

Patients with severe disease reported a higher number of long COVID symptoms which did not however, correlate with cellular immune activation/pro-inflammatory cytokines after adjusting for age, sex and disease severity. Our data suggests that long COVID and persistent immune activation may correlate independently with severe disease.

Source: Marianna Santopaolo, Michaela Gregorova, Fergus Hamilton, David Arnold, Anna Long, Aurora Lacey, Alice Halliday, Holly Baum, Kristy Hamilton, Rachel Milligan, Elizabeth Oliver, Olivia Pearce, Lea Knezevic, Begonia Morales Aza, Alice Milne, Emily Milodowski, Eben Jones, Rajeka Lazarus, Anu Goenka, Adam Finn, Nicholas Maskell, Andrew D Davidson, Kathleen Gillespie, Linda Wooldridge, Laura Rivino (2023) Prolonged T-cell activation and long COVID symptoms independently associate with severe COVID-19 at 3 months eLife 12:e85009 https://doi.org/10.7554/eLife.85009 https://elifesciences.org/articles/85009

Deep Phenotyping of Neurologic Postacute Sequelae of SARS-CoV-2 Infection

Abstract:

Background and Objectives SARS-CoV-2 infection has been associated with a syndrome of long-term neurologic sequelae that is poorly characterized. We aimed to describe and characterize in-depth features of neurologic postacute sequelae of SARS-CoV-2 infection (neuro-PASC).

Methods Between October 2020 and April 2021, 12 participants were seen at the NIH Clinical Center under an observational study to characterize ongoing neurologic abnormalities after SARS-CoV-2 infection. Autonomic function and CSF immunophenotypic analysis were compared with healthy volunteers (HVs) without prior SARS-CoV-2 infection tested using the same methodology.

Results Participants were mostly female (83%), with a mean age of 45 ± 11 years. The median time of evaluation was 9 months after COVID-19 (range 3–12 months), and most (11/12, 92%) had a history of only a mild infection. The most common neuro-PASC symptoms were cognitive difficulties and fatigue, and there was evidence for mild cognitive impairment in half of the patients (MoCA score <26). The majority (83%) had a very disabling disease, with Karnofsky Performance Status ≤80. Smell testing demonstrated different degrees of microsmia in 8 participants (66%). Brain MRI scans were normal, except 1 patient with bilateral olfactory bulb hypoplasia that was likely congenital. CSF analysis showed evidence of unique intrathecal oligoclonal bands in 3 cases (25%). Immunophenotyping of CSF compared with HVs showed that patients with neuro-PASC had lower frequencies of effector memory phenotype both for CD4+ T cells (p < 0.0001) and for CD8+ T cells (p = 0.002), an increased frequency of antibody-secreting B cells (p = 0.009), and increased frequency of cells expressing immune checkpoint molecules. On autonomic testing, there was evidence for decreased baroreflex-cardiovagal gain (p = 0.009) and an increased peripheral resistance during tilt-table testing (p < 0.0001) compared with HVs, without excessive plasma catecholamine responses.

Discussion CSF immune dysregulation and neurocirculatory abnormalities after SARS-CoV-2 infection in the setting of disabling neuro-PASC call for further evaluation to confirm these changes and explore immunomodulatory treatments in the context of clinical trials.

Source: Yair Mina, Yoshimi Enose-Akahata, Dima A. Hammoud, Anthony J. Videckis, Sandeep R. Narpala, Sarah E. O’Connell, Robin Carroll, Bob C. Lin, Cynthia Chen McMahan, Govind Nair, Lauren B. Reoma, Adrian B. McDermott, Brian Walitt, Steven Jacobson, David S. Goldstein, Bryan R. Smith, Avindra Nath. Deep Phenotyping of Neurologic Postacute Sequelae of SARS-CoV-2 Infection. Neurol Neuroimmunol Neuroinflamm Jul 2023, 10 (4) e200097; DOI: 10.1212/NXI.0000000000200097 

Altered Fatty Acid Oxidation in Lymphocyte Populations of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Abstract:

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a disabling multisystem illness in which individuals are plagued with fatigue, inflammatory symptoms, cognitive dysfunction, and the hallmark symptom, post-exertional malaise. While the cause of this disease remains unknown, there is evidence of a potential infectious component that, along with patient symptoms and common onsets of the disease, implicates immune system dysfunction. To further our understanding of the state of ME/CFS lymphocytes, we characterized the role of fatty acids in isolated Natural Killer cells, CD4+ T cells, and CD8+ T cells in circulation and after overnight stimulation, through implicit perturbations to fatty acid oxidation.

We examined samples obtained from at least 8 and as many as 20 subjects for immune cell fatty acid characterization in a variety of experiments and found that all three isolated cell types increased their utilization of lipids and levels of pertinent proteins involved in this metabolic pathway in ME/CFS samples, particularly during higher energy demands and activation. In T cells, we characterized the cell populations contributing to these metabolic shifts, which included CD4+ memory cells, CD4+ effector cells, CD8+ naïve cells, and CD8+ memory cells.

We also discovered that patients with ME/CFS and healthy control samples had significant correlations between measurements of CD4+ T cell fatty acid metabolism and demographic data. These findings provide support for metabolic dysfunction in ME/CFS immune cells. We further hypothesize about the consequences that these altered fuel dependencies may have on T and NK cell effector function, which may shed light on the illness’s mechanism of action.

Source: Maya J, Leddy SM, Gottschalk CG, Peterson DL, Hanson MR. Altered Fatty Acid Oxidation in Lymphocyte Populations of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Int J Mol Sci. 2023 Jan 19;24(3):2010. doi: 10.3390/ijms24032010. PMID: 36768336; PMCID: PMC9916395. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9916395/ (Full text)

Investigating the Genetic and Immunological Aetiology of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Abstract:

This thesis describes two investigations into the disease Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), specifically its genetic aetiology and immune system alterations.

The first study investigated the genetic basis of ME/CFS using Genome-wide Association Studies (GWAS) by attempting to replicate and extend results previously found using UK Biobank cohort data. GWAS attempt to identify associations between DNA variants and phenotypes. T his GWAS was novel, conducted on new phenotypes constructed by combining those in the most up-to-date UK Biobank data release. A new, previously unseen, genome-wide significant association was found on chromosome 6 for males with ME/CFS within the gene PDE10A. Further results were not genome-wide significant, but many were suggestive and hence independent replication may justify further research.

A previous analysis on the UK Biobank cohort had identified an indicative association in females between variants around the SLC25A15 gene at genome-wide significance. I adopted a hypothesis that the dietary protein intake of people with the CFS risk variants would be lower than those with the alternative alleles, due to potentially reduced production of mitochondrial ornithine transporter 1 (ORNT1). However, this association with dietary protein intake was not supported by UK Biobank data.

Additionally, I investigated associations between the human leukocyte antigen (HLA) alleles and the ME/CFS phenotype using UK Biobank data. Associations between alleles within the HLA-C and -DQB1 genes had previously been found in a cohort of Norwegian people with ME/CFS, and my goal was to seek replication of these results in a larger dataset. None of the associations found in the UK Biobank proved to be genome-wide significant.

In my second study I investigated the use of T-cell clonal diversity as a potential biomarker for ME/CFS. This project used cells from CureME Biobank samples in collaboration with Systems Biology Laboratory (SBL). I developed a data analysis pipeline to analyse T-cell receptor (TCR) genomic DNA data based on the best practices currently used in the fields of immunology and mathematical biology. This approach used a mathematical notion of entropy as a measure for the diversity of TCR repertoires, in this way combining all of the most commonly used metrics in mathematical biology. When combined, these measures form a profile for each repertoire, a set of which can be sorted using a machine learning algorithm to partition the repertoires into subgroups.

My hypothesis was that the T-cell clonal expansion of people with ME/CFS would be greater than for healthy controls, and comparable to disease (multiple sclerosis) controls. Although this method was able to effectively classify TCR chains using simulated data, results from experimentally-derived data did not support the hypothesis, with the most effective classifications for both CD4+ and CD8+ cells failing to pass corrections for multiple hypothesis significance testing.

Lay summary

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a disease that affects millions of people around the world. Very little is understood about the cause or progression of the disease, and there is no known cure. At present, there is also no reliable clinical test to determine whether a person has ME/CFS.

This thesis explores the potential for a genetic or immunological basis for ME/CFS, with the goal to eventually find a biomarker that could be used in diagnosis.

The first part of this thesis investigates whether genetic variants are more (or less) common among those with ME/CFS than in the general population. In particular, the region of the genome that encodes immune system proteins was of interest, as previous studies have shown associations between this region and the disease.

Using strict statistical thresholds, none of the previously found associations were replicated. However, one new association was found, with the gene PDE10A, which is implicated in central nervous system diseases, such as Parkinsons and Huntingtons disease. This association has never been seen before, and would require replication in a new cohort before its role in ME/CFS could be confirmed. However, it represents a promising avenue for new research.

The second part of this thesis investigates T-cells. These are highly specialised immune cells in the blood, each of which targets an antigen (foreign substance) such as from a virus. When a T-cell recognises this antigen, it clones itself repeatedly. This clonal expansion is measurable, and can serve as evidence of immune system activation.

My hypothesis was that this immune signature could be used to distinguish people with ME/CFS from healthy controls and others diagnosed with another disease.

I used a mathematical measure of diversity and a machine learning method to sort their immune profiles into groups. However, the pattern of immune activation was not sufficiently clear to provide consistent classification. Hence, the role of the immune system in ME/CFS is still unclear, and the utility of this method as a diagnostic biomarker is not proved.

Source: Joshua James Dibble. Investigating the Genetic and Immunological Aetiology of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. PhD Thesis [University of Edinburgh]  https://era.ed.ac.uk/bitstream/handle/1842/39763/DibbleJJ_2022.pdf?sequence=1&isAllowed=y (Full text)