Cellular and Molecular Studies

1 Cell Culture Studies

In vitro studies using patient-derived cells have provided critical mechanistic insights by isolating cellular defects from whole-body confounders:

  • PBMC bioenergetics: Seahorse extracellular flux analyzer studies consistently show reduced mitochondrial respiration in peripheral blood mononuclear cells (PBMCs) from ME/CFS patients compared to healthy controls (Mandarano et al. 2020) (Tomas et al. 2017). Basal and maximal respiration, spare respiratory capacity, and ATP-linked respiration are all reduced. Critically, these deficits persist in cultured cells removed from the patient’s systemic environment, suggesting a cell-intrinsic metabolic defect rather than a consequence of circulating factors alone
  • Metabolic flux analysis: Fluge et al. (2016) demonstrated that ME/CFS patient serum inhibits pyruvate dehydrogenase (PDH) activity in healthy muscle cells, suggesting a circulating inhibitory factor. PDH inhibition would impair the conversion of pyruvate to acetyl-CoA, forcing reliance on anaerobic glycolysis even in the presence of adequate oxygen—consistent with the “metabolic trap” hypothesis. A 2025 biofabricated 3D skeletal-muscle model independently confirmed that patient serum (ME/CFS and Long COVID) induces the same glycolytic shift and a biphasic metabolic fragility in otherwise-healthy contracting muscle (see A Circulating Serum Factor Reproduces the ME/CFS Muscle Metabolic Phenotype in Healthy Tissue and A Three-Phase Model: PDH Compensation, Cofactor Exhaustion, Mitochondrial Collapse), strengthening the circulating-factor interpretation. Post-exertional muscle biopsy data likewise show glycolytic fiber shift and metabolic disturbance (Appelman et al. 2024).
  • NK cell function: Reduced NK cell cytotoxicity is one of the most replicated findings in ME/CFS (Hardcastle et al. 2016). Cell culture studies demonstrate both reduced killing capacity and impaired calcium signaling through TRPM3 ion channels (Cabanas et al. 2021)
  • T cell stimulation: Patient-derived T cells show altered metabolic responses to stimulation, with reduced glycolytic reserve and impaired ability to upregulate oxidative phosphorylation upon activation—consistent with the T cell exhaustion phenotype documented in vivo

2 Animal Models

Animal models for ME/CFS have been historically limited by the difficulty of replicating a complex, multi-system human disease in laboratory animals. Most existing models target individual pathways rather than the full syndrome.

2.1 Existing Approaches and Limitations

Rodent models using viral infection (murine gammaherpesvirus (Olivadoti et al. 2011) (Dong, Forrest, and Liang 2017), poly(I:C) injection (Cunningham et al. 2007) (Foster et al. 2021)), immune activation (LPS administration (Zhang et al. 2016) (Foster et al. 2021)), or forced exercise (Ohba et al. 2019) have reproduced individual ME/CFS features—fatigue-like behavior, neuroinflammation, or immune activation—but none recapitulates the defining feature of post-exertional malaise with delayed onset and prolonged recovery. Key limitations include:

  • Artificial induction: Laboratory infection or chemical challenge does not replicate the natural triggering events (viral infection in a genetically susceptible host) that produce human ME/CFS.
  • PEM measurement: No validated method exists for quantifying PEM in rodents. Activity monitoring can detect reduced voluntary wheel running, but distinguishing pathological exercise intolerance from sickness behavior or learned avoidance is methodologically difficult.
  • Chronicity: Most models produce acute effects lasting days to weeks, whereas ME/CFS is defined by persistence over months to years.
  • Multi-system involvement: Models targeting a single pathway (e.g., neuroinflammation) cannot reproduce the simultaneous immune, metabolic, autonomic, and neurological dysfunction that characterizes ME/CFS.

2.2 Feline Infectious Peritonitis as a Comparative Coronavirus Model

The Kol et al. (2026) discovery that feline infectious peritonitis virus (FIPV) persists in B and T lymphocytes after antiviral treatment and clinical recovery (Kol et al. 2026) establishes FIP as a uniquely valuable comparative model for post-viral immune dysfunction. Unlike artificial rodent models, FIP is a naturally occurring coronavirus disease with several features directly relevant to post-COVID ME/CFS:

  • Natural coronavirus infection: FIPV is a feline coronavirus that produces systemic immune dysfunction without artificial induction.

  • Immune cell tropism: FIPV replicates in macrophages, B cells, and T cells—paralleling the suspected SARS-CoV-2 tropism for immune cells in long COVID.

  • Post-treatment viral persistence: Viral RNA persists in lymphocytes after antiviral treatment (GS-441524) and resolution of clinical signs, modeling the hypothesized viral reservoir in human ME/CFS (Speculation Lymphocyte Reservoir Ratchet).

  • Accessible lymphoid tissue: Unlike human studies, feline lymph node tissue can be directly examined, enabling mechanistic studies of viral–immune cell interactions impossible in human subjects.

  • Treatment response monitoring: Cats treated with GS-441524 (a nucleoside analog related to remdesivir) can be monitored longitudinally for immune recovery, relapse, and persistent dysfunction. Proposed Research Directions.

  • Longitudinal immune profiling: Track immune cell phenotype, function, and viral RNA persistence in FIP-recovered cats over 12–24 months post-treatment. Determine whether persistent lymphocyte infection correlates with chronic immune dysfunction analogous to ME/CFS T cell exhaustion.

  • Activity monitoring: Implement accelerometry-based activity tracking in FIP-recovered cats to determine whether a subgroup develops persistent activity reduction or post-exertional deterioration analogous to PEM.

  • Metabolic profiling: Compare immune cell bioenergetics (Seahorse analysis) between FIP-recovered cats with persistent viral RNA versus those who clear virus completely, testing whether viral persistence drives immune cell metabolic dysfunction (as proposed in Hypothesis Immune Cell Energy Starvation Creates a Viral Persistence Niche).

  • Intervention testing: Use the FIP model to test combined antiviral + metabolic support strategies before human trials, determining whether metabolic supplementation enhances viral clearance from lymphocytes.

References

Appelman, Brent, Braeden T. Charlton, Richie P. Goulding, Tom J. Kerkhoff, Ellen A. Breedveld, Wendy Noort, Carla Offringa, et al. 2024. “Muscle Abnormalities Worsen After Post-Exertional Malaise in Long COVID.” Nature Communications 15: 17. https://doi.org/10.1038/s41467-023-44432-3.
Cabanas, Helene, Katsuhiko Muraki, Natalie Eaton-Fitch, Donald R Staines, and Sonya Marshall-Gradisnik. 2021. “Low Dose Naltrexone Restores TRPM3 Ion Channel Function in Natural Killer Cells from Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Patients.” Frontiers in Immunology 12: 687806. https://doi.org/10.3389/fimmu.2021.687806.
Cunningham, Colm, Sarah Campion, Jessica Teeling, Lisa Felton, and V. Hugh Perry. 2007. “The Sickness Behaviour and CNS Inflammatory Mediator Profile Induced by Systemic Challenge of Mice with Synthetic Double-Stranded RNA (Poly I:C).” Brain, Behavior, and Immunity 21 (4): 490–502. https://doi.org/10.1016/j.bbi.2006.12.007.
Dong, Shiyou, J. Craig Forrest, and Xiaozhen Liang. 2017. “Murine Gammaherpesvirus 68: A Small Animal Model for Gammaherpesvirus-Associated Diseases.” In Advances in Experimental Medicine and Biology, 1018:225–36. Singapore: Springer. https://doi.org/10.1007/978-981-10-5765-6_14.
Foster, Courtney G., Lawrence M. Landowski, Brad A. Sutherland, and David W. Howells. 2021. “Differences in Fatigue-Like Behavior in the Lipopolysaccharide and Poly I:C Inflammatory Animal Models.” Physiology & Behavior 232: 113347. https://doi.org/10.1016/j.physbeh.2021.113347.
Hardcastle, Susan L, Ekua W Brenu, Samantha Johnston, Thao Nguyen, Teilah Huth, Maninder Kaur, Sandra B Ramos, et al. 2016. “Novel Characterisation of Mast Cell Phenotypes from Peripheral Blood Mononuclear Cells in Chronic Fatigue Syndrome/Myalgic Encephalomyelitis Patients.” BMC Immunology 17 (1): Article 30. https://doi.org/10.1186/s12865-016-0167-z.
Kol, Amir et al. 2026. “Beyond Macrophages: FIPV Tropism Includes T and B Lymphocytes.” Veterinary Microbiology 313: 110864. https://doi.org/10.1016/j.vetmic.2025.110864.
Mandarano, Alexandra H., Jessica Maya, Ludovic Giloteaux, Daniel L. Peterson, Marco Maynard, C. Gunnar Gottschalk, and Maureen R. Hanson. 2020. “Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Patients Exhibit Altered t Cell Metabolism and Cytokine Associations.” Journal of Clinical Investigation 130 (3): 1491–1505. https://doi.org/10.1172/JCI132185.
Ohba, Tsuyoshi, Saki Domoto, Masashi Tanaka, Shinsuke Nakamura, Masamitsu Shimazawa, and Hideaki Hara. 2019. “Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Induced by Repeated Forced Swimming in Mice.” Biological & Pharmaceutical Bulletin 42 (7): 1140–45. https://doi.org/10.1248/bpb.b19-00009.
Olivadoti, Melissa D., Jason B. Weinberg, Linda A. Toth, and Mark R. Opp. 2011. “Sleep and Fatigue in Mice Infected with Murine Gammaherpesvirus 68.” Brain, Behavior, and Immunity 25 (4): 696–705. https://doi.org/10.1016/j.bbi.2011.01.010.
Tomas, Cara, Andreas Finkelmeyer, Tim Hodgson, Laura MacLachlan, Guy A. MacGowan, Andrew M. Blamire, and Julia L. Newton. 2017. “Elevated Brain Natriuretic Peptide Levels in Chronic Fatigue Syndrome Associate with Cardiac Dysfunction: A Case Control Study.” Open Heart 4 (2): e000697. https://doi.org/10.1136/openhrt-2017-000697.
Zhang, Zhi-Tao, Xin-Miao Du, Xiao-Jun Ma, Yuan Zong, Jia-Kun Chen, Chun-Lei Yu, You-Gui Liu, Yu-Cai Chen, Li-Juan Zhao, and Guang-Cheng Lu. 2016. “Activation of the NLRP3 Inflammasome in Lipopolysaccharide-Induced Mouse Fatigue and Its Relevance to Chronic Fatigue Syndrome.” Journal of Neuroinflammation 13: 71. https://doi.org/10.1186/s12974-016-0539-1.