ME/CFS and the Immune System: Cytokines, NK Cells, and Immune Dysregulation

For decades, ME/CFS was dismissed as a psychological condition because no consistent biological abnormality could be identified. That has changed dramatically over the past decade. A growing body of research has documented specific, reproducible immune abnormalities in ME/CFS patients — abnormalities that help explain the characteristic symptoms of the illness and point toward potential treatment targets.

Cytokine Dysregulation

Cytokines are signaling proteins that coordinate the immune response. In ME/CFS, multiple studies have found abnormal cytokine profiles, though the specific pattern varies between studies and patient subgroups.

Key findings include:

• Elevated pro-inflammatory cytokines: Interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and interleukin-1 beta (IL-1β) are elevated in some ME/CFS patient subgroups, suggesting ongoing low-grade inflammation.
• TGF-β elevation: Transforming growth factor-beta, which has both anti-inflammatory and pro-fibrotic effects, is consistently elevated in ME/CFS. TGF-β can suppress T cell function and contribute to immune exhaustion.
• Interferon signature: Some ME/CFS patients show an elevated interferon signature (a pattern of gene expression driven by interferon signaling), similar to that seen in autoimmune conditions like lupus and in viral infections.
• Cytokine patterns correlating with severity: A landmark 2017 study by Hornig et al. found that cytokine patterns in ME/CFS changed with disease duration — early-stage patients showed elevated pro-inflammatory cytokines, while long-duration patients showed immune exhaustion patterns. This suggests the immune response evolves over the course of the illness.

Natural Killer Cell Dysfunction

Natural killer (NK) cells are innate immune cells that provide rapid defense against viral infections and cancer. They are among the most consistently abnormal immune cells in ME/CFS.

Key NK cell abnormalities in ME/CFS:

• Reduced cytotoxic function: ME/CFS patients consistently show reduced NK cell cytotoxicity — the ability of NK cells to kill infected or abnormal cells. This is one of the most replicated findings in ME/CFS immunology.
• Altered receptor expression: NK cells in ME/CFS show abnormal expression of activating and inhibitory receptors, suggesting dysregulation of their activation threshold.
• Reduced NK cell numbers: Some studies find reduced circulating NK cell counts, while others find normal counts with reduced function.

The consistent finding of NK cell dysfunction is significant because it suggests impaired antiviral immunity — which could explain both the viral trigger of ME/CFS and the susceptibility to reactivation of latent herpesviruses (EBV, HHV-6) that has been documented in ME/CFS patients.

T Cell Abnormalities

T cells — the adaptive immune cells that provide targeted responses to specific pathogens — also show abnormalities in ME/CFS:

• T cell exhaustion: Similar to what has been found in Long COVID, ME/CFS patients show markers of T cell exhaustion (PD-1, TIM-3 expression), suggesting chronic antigen stimulation.
• Regulatory T cell dysfunction: Regulatory T cells (Tregs) normally suppress excessive immune responses. Some studies find abnormal Treg function in ME/CFS, which could contribute to both autoimmune features and chronic inflammation.
• Metabolic dysfunction in T cells: A landmark 2019 study by Mandarano et al. found that T cells from ME/CFS patients have impaired mitochondrial function and altered metabolic profiles, with reduced capacity for oxidative phosphorylation. This finding connects immune dysfunction to the broader metabolic abnormalities in ME/CFS.

Autoantibodies in ME/CFS

Multiple studies have found elevated autoantibodies in ME/CFS patients, including:

• Anti-beta-adrenergic receptor antibodies: Targeting receptors that regulate heart rate and blood pressure — potentially explaining the dysautonomia common in ME/CFS
• Anti-muscarinic receptor antibodies: Targeting receptors in the autonomic nervous system
• Anti-nuclear antibodies (ANA): Present in a subset of ME/CFS patients, suggesting autoimmune features

The presence of autoantibodies targeting autonomic receptors has led to trials of immunoadsorption (a process that removes autoantibodies from the blood) in ME/CFS patients. Early results from German trials have been promising, though larger controlled trials are needed.

Mast Cell Activation

Mast cell activation is increasingly recognized as a feature of ME/CFS, particularly in patients with overlapping MCAS. Mast cells are innate immune cells that release histamine, prostaglandins, and other inflammatory mediators when activated. In ME/CFS, mast cell activation may contribute to:

• Widespread inflammation and pain
• Gastrointestinal symptoms
• Neurological symptoms (mast cells are present in the brain and can affect neuroinflammation)
• Autonomic dysregulation

Neuroinflammation

Perhaps the most clinically significant immune finding in ME/CFS is neuroinflammation — inflammation within the central nervous system. A 2014 Japanese PET scan study by Nakatomi et al. found significantly elevated neuroinflammation markers in ME/CFS patients compared to controls, particularly in the cingulate cortex, hippocampus, amygdala, thalamus, midbrain, and pons — regions involved in cognition, pain processing, and autonomic regulation.

This neuroinflammation finding helps explain the cognitive symptoms, pain amplification, and autonomic dysfunction of ME/CFS, and points toward anti-neuroinflammatory treatments (such as low-dose naltrexone) as potentially beneficial.

What This Means for Treatment

The immune abnormalities in ME/CFS are not yet consistently targetable with approved treatments, but several approaches are being explored:

• Low-dose naltrexone: Reduces microglial activation and neuroinflammation
• IVIG: For patients with autoantibodies or evidence of immune deficiency
• Rituximab: A B cell-depleting antibody that was tested in ME/CFS (results were mixed in the large Norwegian trial, but subgroup analyses suggested benefit in some patients)
• Immunoadsorption: Removes autoantibodies; promising early results
• Antivirals: For patients with evidence of herpesvirus reactivation

The immune complexity of ME/CFS means that treatment is unlikely to be one-size-fits-all. Immune profiling — identifying which specific abnormalities are present in a given patient — is likely to be essential for precision treatment selection.