Despite their dramatic name, natural killer (NK) cells are actually a very important part of our immune system and help protect us from viruses by killing cells that have been infected. They can also target tumour cells.

There is evidence to suggest that the cytotoxicity of NK cells (that is, their ability to destroy other cells) is compromised in some people with ME/CFS, which would have an impact on how well these individuals can fight off infections.

A group of researchers from Griffith University on the Gold Coast of Australia recently confirmed this finding by systematically reviewing the results of seventeen studies that compared the characteristics of NK cells between ME/CFS patients and healthy control subjects.

The paper was published in the journal Systematic Reviews.

NK cell cytotoxicity – measured by flow cytometry or a chromium-51 release assay – was consistently impaired in patients across these studies, and one study also reported a reduction in cytotoxicity over the course of 12 months of follow-up.

Other characteristics of NK cells ­– such as immunophenotype, degranulation, lytic proteins and cytokine production – were also investigated, but the results were not consistent.

The researchers conclude that NK cell cytotoxicity can be impaired in people with ME/CFS, and may represent a biomarker that could help define a subgroup from within this fairly broad sample of patients (most of whom were diagnosed using the Fukuda criteria).

They also suggest that further research into the immunological consequences of ME/CFS is warranted.