Myalgic encephalomyelitis, also referred to as chronic fatigue syndrome (ME/CFS), is a debilitating condition with unknown etiology that is characterized by excessive and persistent fatigue with physical or mental exertion, often accompanied by flu-like symptoms, and not relieved by rest. Previous clinical studies suggest that infections caused by intracellular pathogens, such as Epstein-Barr virus, may elicit ME/CFS. Therefore, predisposition to the development of ME/CFS may be associated with an impairment of the immune system.
Cytotoxic T cells are crucial in the immunologic response to infections, but their role in ME/CFS is not fully known. Factors such as psychological or physical stress also trigger ME/CFS, and stress can negatively affect cytotoxic T cells. To better determine if cytotoxic T cell impairment is associated with ME/CFS, a study of T cell phenotype and function was conducted in patients with ME/CFS and healthy controls.
Flow cytometry analysis of patient and control blood showed no significant differences in the absolute numbers of NK and cytotoxic T cells. The levels of cytotoxic granules in NK and cytotoxic T cells were also assessed by flow cytometry using antibodies to lineage markers and intracellular perforin and granzymes A and B. There were no differences in expression levels of granule components between the two patient groups. To evaluate cytotoxic T and NK function, a measurement of the exocytic capacity of stimulated (using a mastocytoma cell line) cytotoxic T and NK cell subsets was performed. The cells were stained with lineage markers and a marker for immune cell degranulation (CD107a), followed by flow cytometry. No differences in cytotoxic T cell and NK cell function were found between ME/CFS and control samples.
Using antibodies to interferon (IFN)-gamma and tumor necrosis factor (TNF) showed more IFN-gamma (but not TNF) after stimulation of NK cells (not cytotoxic T cells) in the ME/CFS samples compared to controls. However, this effect was not statistically significant after correction for multiple testing. Taken together, the study results suggest that cytotoxic T cell status is not impaired in those with ME/CFS and is not likely linked to its etiology. Therefore, T cell characteristics would not serve as feasible biomarkers of ME/CFS for diagnostic purposes.
Theorell, J., Bileviciute-Ljungar, I., Tesi, B., Schlums, H., Johnsgaard, M., & Asadi-Azarbaijani, B. et al. (2017). Unperturbed Cytotoxic Lymphocyte Phenotype and Function in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Patients. Frontiers In Immunology, 8. doi:10.3389/fimmu.2017.00723