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Low NK Cell Activity in Chronic Fatigue Syndrome (CFS) and Relationship to Symptom Severity

David Strayer, Victoria Scott and William Carter

Background: Natural killer (NK) cells act as an immune surveillance against invading pathogens and tumors. NK cell cytotoxicity (NKCC) has been reported to be decreased in patients with CFS.
Methods: The objective of this review was to conduct an analysis of available publications that reported NKCC data in CFS in order to evaluate any relationships to case definitions used to define CFS and symptom severity.
Results: Of 17 studies that evaluated NKCC in patients with CFS, defined using the CDC 1988 and/or 1994 case definition (CD), 88% (15/17) concluded that NKCC was decreased in CFS patients compared to normal controls. The NKCC decrease was seen using two established methods, 51Cr release (11/13) and flow cytometry (4/4). The mean percent decrease in NKCC using the CDC 1988 CD (66.3%) was significantly greater than that using the CDC 1994 CD (49.7%) (p<0.01). This result is consistent with that of six publications showing a greater decrease in NKCC associated with increased CFS symptom severity based on the lower symptom requirement for the CDC 1994 vs. 1988 CD. In contrast, there was no significant difference in the mean percent decrease in NKCC seen comparing the CDC 1994 CD defined population using the 51Cr release (48.3%) vs. flow cytometry (50.7%) assays (p>0.5). Finally, seven studies investigating the ability of various agents to augment NKCC in patients with CFS showed increases of NKCC with both in vitro exposure (4/5) and in vivo exposure using randomized trials (2/2).
Conclusions: Low NKCC is commonly seen in CFS and is associated with increase symptom severity.