Natural killer cell function in chronic fatigue syndrome

Chronic fatigue syndrome (CFS) is currently defined by clinical signs and symptoms including debilitating fatigue that is not attributable to other known clinical conditions, by flu-like symptoms (e.g., pharyngitis, adenopathy, low-grade fever, myalgia, arthralgia, headache) and by neuropsychological manifestations (e.g., difficulty concentrating, exercise intolerance, and sleep disturbances). CFS is frequently of sudden onset. Its etiology is unknown. Although immunologic abnormalities are frequently described in the literature of CFS, there is a lack of consensus, and, as of yet, no immunological dysfunctions are part of the existing case definition. This review examines one aspect of the literature, that dealing with natural killer (NK) cell function. A surprising amount of concurrence is found supporting the view that NK cell activity is depressed in CFS patients. Data are presented that suggest a methodology consisting of a whole blood cytotoxicity assay, combined with flow cytometric enumeration of NK cell numbers, would allow interlaboratory comparisons to be made and would be useful in research studies on this perplexing syndrome.