Chronic fatigue syndrome and circulating cytokines: A systematic review.
Blundell, S, Ray, K K, Buckland, M et al. · Brain, behavior, and immunity · 2015 · DOI
Quick Summary
Researchers reviewed 38 studies looking at whether immune proteins called cytokines are elevated in people with ME/CFS. They found that one specific cytokine, TGF-β, was consistently higher in people with ME/CFS compared to healthy people in about 63% of studies. However, most other immune proteins measured were normal, and exercise did not change cytokine levels differently between people with ME/CFS and healthy controls.
Why It Matters
Understanding whether immune dysregulation drives ME/CFS is crucial for developing targeted treatments. This review clarifies that circulating cytokines alone do not explain the hallmark post-exertional malaise symptom, but identifies TGF-β as a candidate for further investigation, potentially redirecting research toward more specific immune mechanisms.
Observed Findings
TGF-β was significantly elevated in 5 of 8 studies (63%) examining ME/CFS patients compared to controls
No other individual cytokines showed abnormal concentrations in the majority of studies reviewed
Physical exercise produced no significant differences in circulating cytokine levels between ME/CFS cases and healthy controls
Elevated TGF-β concentrations were not altered by acute physical exercise in ME/CFS patients
77 different serum or plasma cytokines were measured across the included studies without immune stimulation
Inferred Conclusions
Circulating cytokine abnormalities do not adequately explain the core characteristic of post-exertional fatigue in ME/CFS
TGF-β elevation at biologically relevant levels warrants further targeted investigation as a potential immune biomarker
The lack of exercise-induced cytokine changes suggests post-exertional malaise may involve immune mechanisms beyond simple circulating cytokine responses
Measuring cytokines from blood alone may be insufficient to detect immune dysfunction in ME/CFS
Remaining Questions
What is the functional significance of elevated TGF-β and does it contribute to symptom generation or disease mechanisms?
What This Study Does Not Prove
This review does not prove that cytokines play no role in ME/CFS—it shows that abnormal circulating levels are not the primary explanation. Elevated TGF-β correlation does not establish causation. The study also cannot determine whether other immune markers (intracellular cytokines, tissue-level inflammation, or immune cell subsets) might be abnormal, as it focused only on serum and plasma measurements.
Why does TGF-β remain elevated or unchanged with exercise when other potential immune responses might occur?
Would examining intracellular cytokine production, tissue-level inflammation, or specific immune cell populations reveal abnormalities not detected by serum measurements?
How do findings of elevated TGF-β integrate with other proposed ME/CFS pathophysiological mechanisms such as mitochondrial dysfunction or viral persistence?