title: Impaired natural immunity, cognitive dysfunction, and physical symptoms in patients with chronic fatigue syndrome: preliminary evidence for a subgroup?
abstract: OBJECTIVE
  The diagnostic criteria of chronic fatigue syndrome (CFS) define a heterogeneous population composed of several subgroups. Past efforts to identify subgroup markers have met with mixed success. This study was designed to examine natural killer cell activity (NKCA) as a potential subgroup marker by comparing the clinical presentations of CFS patients with and without clinically reduced NKCA.
  
  
  METHODS
  Forty-one female CFS patients were classified into having either low or normal NKCA levels. These subgroups were then compared on objective measures of cognitive functioning and subjective assessments of fatigue, vigor, cognitive impairment, and daytime dysfunction.
  
  
  RESULTS
  Relative to CFS patients in the normal-NKCA subgroup, low-NKCA patients reported less vigor, more daytime dysfunction, and more cognitive impairment. In addition, low-NKCA patients performed less on objective measures of cognitive functioning relative to normal-NKCA patients.
  
  
  CONCLUSIONS
  The results are offered as preliminary evidence in support of using NKCA as an immunological subgroup marker in CFS. Findings are also discussed in terms of known associations between dysregulated immune functions, somatic symptoms, and psychological stress.
authors.affiliation: Department of Psychology, Behavioral Medicine Research Center, University of Miami, FL, USA.
authors.forename: Scott D
authors.initials: SD
authors.lastname: Siegel
authors.forename: Michael H
authors.initials: MH
authors.lastname: Antoni
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Fletcher
authors.forename: Kevin
authors.initials: K
authors.lastname: Maher
authors.forename: Mary Catherine
authors.initials: MC
authors.lastname: Segota
authors.forename: Nancy
authors.initials: N
authors.lastname: Klimas
mesh_terms: D000293:Adolescent; D000328:Adult; D003072:Cognition Disorders / Q000175:diagnosis* / Q000276:immunology; D015673:Fatigue Syndrome, Chronic / Q000175:diagnosis* / Q000276:immunology; D005260:Female; D006801:Humans; D007113:Immunity, Innate / Q000276:immunology*; D020014:K562 Cells / Q000276:immunology; D007694:Killer Cells, Natural / Q000276:immunology; D008137:Longitudinal Studies; D018655:Lymphocyte Count; D008875:Middle Aged; D009483:Neuropsychological Tests; D012016:Reference Values; D012803:Sick Role; D013001:Somatoform Disorders / Q000175:diagnosis / Q000276:immunology