Immunological Studies
Immunological research has provided some of the most consistent and replicated findings in ME/CFS: NK cell dysfunction: Reduced NK cell cytotoxic activity is the most replicated immunological finding in ME/CFS, confirmed across multiple independent laboratories and cohorts (Hardcastle et al. 2016). The defect involves both reduced numbers of cytotoxic NK cell subsets (CD56dimCD16+) and impaired per-cell killing capacity, linked to defective calcium signaling through TRPM3 ion channels (Cabanas et al. 2021). T cell abnormalities: Multiple studies document altered CD4+/CD8+ ratios, increased expression of activation and exhaustion markers (CD38, HLA-DR, PD-1, Tim-3), and reduced proliferative capacity. The NIH deep phenotyping study found elevated CD8+ T cell PD-1 expression consistent with chronic antigenic stimulation (Walitt et al. 2024). Iu et al. (2024) provided transcriptomic and epigenetic evidence for extensive T cell exhaustion (Iu et al. 2024). Cytokine profiles: Hornig et al. (2015) identified distinct cytokine signatures that vary with disease duration: elevated pro-inflammatory cytokines (IL-6, TNF-\(\alpha\), IL-1\(\beta\)) in early disease (\(\leq\) 3 years) transitioning to a mixed or suppressed profile in chronic disease (Hornig et al. 2015). Montoya et al. (2017) confirmed cytokine–severity correlations (Montoya et al. 2017). However, cytokine findings remain inconsistent across laboratories, partly due to methodological differences in sample handling, assay platforms, and patient selection. Autoantibody discovery: Loebel et al. (2016) and subsequent studies identified elevated autoantibodies against G protein-coupled receptors (GPCRs), including \(\beta_2\)-adrenergic, muscarinic M3/M4, and angiotensin II AT1 receptors (Loebel et al. 2016) (Freitag et al. 2021) (Bynke et al. 2020). Azcue et al. (2026) provide the most comprehensive concurrent autonomic and cognitive testing alongside GPCR AAb measurement: \(\beta_2\)-adrenergic AAb titers correlate with sympathovagal imbalance (\(r=0.45\), \(p=0.001\)) while muscarinic M1, M3, M4 AAbs correlate positively with verbal and working memory in \(n=59\) ME/CFS (Azcue et al. 2026). These autoantibodies provide a mechanistic link between immune dysfunction and autonomic symptoms. Their functional significance is supported by the clinical response to immunoadsorption in some patients. Viral persistence: Evidence for persistent viral infection in ME/CFS includes elevated antibody titers against EBV, HHV-6, and CMV in subgroups of patients, detection of viral DNA/RNA in tissue samples, and the FIP model of post-viral lymphocyte persistence (Kol et al. 2026). Whether viral persistence is causative or an epiphenomenon of immune dysfunction remains an active research question.