A systematic review of natural killer cells profile and cytotoxic function in myalgic encephalomyelitis/chronic fatigue syndrome.
Eaton-Fitch, Natalie, du Preez, Stanley, Cabanas, Hélène et al. · Systematic reviews · 2019 · DOI
Quick Summary
This review examined research on natural killer cells, which are immune cells that help fight infections and abnormal cells in the body. Scientists found that people with ME/CFS consistently have natural killer cells that don't work as well as they should. This discovery was the most reliable and consistent finding across all the studies reviewed, suggesting it could be an important marker for understanding ME/CFS.
Why It Matters
Identifying a consistent immune abnormality in ME/CFS is crucial because it provides objective evidence of biological dysfunction and could help validate the disease as a real medical condition rather than a psychological disorder. If NK cell dysfunction proves reliable across patients, it might eventually be used as a diagnostic marker or therapeutic target for treatment development. This research offers hope that understanding immune mechanisms could lead to better management strategies for ME/CFS patients.
Observed Findings
Impaired NK cell cytotoxicity was documented in all 17 reviewed studies with consistent methodology—making it the most reliable immunological marker identified.
Aberrations in NK cell lytic protein levels (proteins involved in cell killing) were reported across multiple studies.
Significant heterogeneity existed between studies in other measured outcomes, including NK cell phenotype, receptor expression, cytokine production, and degranulation patterns.
Only 11 of 17 studies specifically investigated cytotoxicity, while 14 examined phenotype/receptor profiles and fewer examined cytokine production (3 studies) or degranulation (4 studies).
All included studies were observational case-control designs with no randomized controlled trials identified.
Inferred Conclusions
Impaired NK cell cytotoxicity is a reliable and consistent biomarker suitable for continued ME/CFS research and potentially useful as a cellular model for the disease.
NK cell abnormalities may characterize a biologically-defined subset of ME/CFS patients, reflecting the disease's known heterogeneity.
Future research should focus on standardizing methodology to clarify which NK cell features beyond cytotoxicity are most relevant to ME/CFS pathology.
Remaining Questions
Does NK cell dysfunction cause ME/CFS symptoms, or is it a consequence of the disease process—and can improving NK function improve clinical outcomes?
What This Study Does Not Prove
This review does not prove that NK cell dysfunction causes ME/CFS or that correcting it would cure the disease—only that an association exists. The heterogeneity in findings suggests NK cell abnormalities may characterize only a subset of ME/CFS patients rather than all affected individuals. The study design (reviewing observational studies) cannot establish causation, and the variability in how different studies measured NK function limits definitive conclusions about which specific NK cell features are most important.
Which specific subset of ME/CFS patients exhibits NK cell abnormalities, and do these patients have distinct clinical characteristics or prognoses?
What mechanisms drive the impaired cytotoxicity in ME/CFS NK cells, and are they reversible with targeted interventions?
Why do other NK cell features (phenotype, receptors, cytokine production) show inconsistent abnormalities across studies—reflecting true biological heterogeneity or methodological variation?