title: Clinicopathological and phenotypic features of chronic NK cell lymphocytosis identified among patients with asymptomatic lymphocytosis.
abstract: BACKGROUND
  Chronic natural killer (NK) cell lymphocytosis is currently a provisional entity. This study demonstrated NK cell lymphocytosis in patients with asymptomatic lymphocytosis and presented the hematological and phenotypic findings.
  
  
  METHODS
  Flow cytometry analysis was performed for investigation of unexplained peripheral lymphocytosis. NK cells were determined by the phenotype of CD3-/CD16+/CD56+. Chronic NK cell lymphocytosis was defined by a NK cell count of ≥ 2 × 10(9)/L, persistent for over 6 months, no evidence of B- or T-cell clonality and no hematologic disorders.
  
  
  RESULTS
  Among 190 patients with peripheral lymphocytosis, 15(7.9%) patients, age 42-72 years, were identified to have NK cell lymphocytosis, with a median NK cell count of 3.1 × 10(9)/L (range 2.1-7.3 × 10(9)/L). Persistent NK cell lymphocytosis was confirmed with a median follow-up of 18 months. CD56(bright) NK cell populations were seen in eight patients and CD56(dim) NK cells in seven patients. CD57 co-expression was seen in both CD56(dim) and CD56(bright) cells. CD7, CD2, or CD8 expression was seen in some of the NK populations. The NK cell lymphocytosis appeared stable and no progression to NK cell leukemia during the follow-up period.
  
  
  CONCLUSIONS
  This study demonstrated that chronic NK cell lymphocytosis, similar to monoclonal B lymphocytosis or T-cell clones, may account for asymptomatic lymphocytosis. There were no identifiable causes of the NK cell expansion. The variable phenotype may represent the heterogeneity and pathological features of NK lymphocytosis.
authors.affiliation: Alkali Soil Natural Environmental Science Center, Northeast Forestry University, Key Laboratory of Saline-alkali Vegetation Ecology Restoration, Ministry of Education, Harbin, China.|Central Laboratory, Department of Hematology, The First Hospital of Harbin Medical University, Harbin, China.
authors.forename: F
authors.initials: F
authors.lastname: Cao
authors.affiliation: Central Laboratory, Department of Hematology, The First Hospital of Harbin Medical University, Harbin, China.
authors.forename: H
authors.initials: H
authors.lastname: Zhao
authors.affiliation: Central Laboratory, Department of Hematology, The First Hospital of Harbin Medical University, Harbin, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Li
authors.affiliation: Alkali Soil Natural Environmental Science Center, Northeast Forestry University, Key Laboratory of Saline-alkali Vegetation Ecology Restoration, Ministry of Education, Harbin, China.
authors.forename: S
authors.initials: S
authors.lastname: Dai
authors.affiliation: Central Laboratory, Department of Hematology, The First Hospital of Harbin Medical University, Harbin, China.
authors.forename: C
authors.initials: C
authors.lastname: Wang
mesh_terms: D000328:Adult; D000368:Aged; D015703:Antigens, CD / Q000378:metabolism; D058070:Asymptomatic Diseases; D015415:Biomarkers; D002908:Chronic Disease; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D016130:Immunophenotyping; D007694:Killer Cells, Natural / Q000378:metabolism / Q000473:pathology*; D008218:Lymphocytosis / Q000097:blood / Q000175:diagnosis* / Q000473:pathology; D008297:Male; D008875:Middle Aged
chemical_list: D015703:Antigens, CD; D015415:Biomarkers
keywords: CD56; CD57; Natural killer cells; aberrant phenotype; lymphocytosis