title: Increased levels of interleukin-16 in the airways of tobacco smokers: relationship with peripheral blood T lymphocytes.
abstract: BACKGROUND
  The mechanisms behind the development of systemic immunomodulation among tobacco smokers are not fully understood, but several studies have indicated a role for CD8+ and/or CD4+ T cells. Interleukin (IL)-16, a cytokine released from inflammatory cells as well as bronchial epithelial cells, can recruit and activate CD4+ T cells. A study was undertaken to establish whether the IL-16 level is increased in the airways of tobacco smokers and to determine whether airway levels of IL-16 are related to the number and function of systemic T lymphocytes.
  
  
  METHODS
  Bronchoalveolar lavage (BAL) fluid was collected from eight never smokers and 18 tobacco smokers without clinical airway symptoms, and from 16 tobacco smokers with clinical airway symptoms. Interleukin-16 protein levels in BAL fluid were determined using enzyme-linked immunosorbent assay (ELISA). Peripheral blood was collected for determination of CD4+ T cell content using flow cytometry. The responsiveness of systemic lymphocytes in smokers was assessed by measuring the proliferative response of peripheral blood lymphocytes to the superantigen staphylococcus enterotoxin A (SEA).
  
  
  RESULTS
  The IL-16 protein level in the BAL fluid was significantly higher in tobacco smokers than in non-smokers. However, among tobacco smokers the IL-16 level was similar in asymptomatic smokers and in those with airway symptoms. The level of IL-16 in the BAL fluid of smokers correlated negatively with the percentage of CD4+ T cells and positively with superantigen stimulated lymphocyte proliferation in peripheral blood.
  
  
  CONCLUSIONS
  In tobacco smokers the airway IL-16 level is increased and it is possible that this increase in IL-16 influences systemic immunomodulation by altering the number and responsiveness of systemic T lymphocytes.
authors.affiliation: Department of Respiratory Medicine and Allergology, S-413 46 Gothenburg, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Laan
authors.forename: I
authors.initials: I
authors.lastname: Qvarfordt
authors.forename: G C
authors.initials: GC
authors.lastname: Riise
authors.forename: B A
authors.initials: BA
authors.lastname: Andersson
authors.forename: S
authors.initials: S
authors.lastname: Larsson
authors.forename: A
authors.initials: A
authors.lastname: Lindén
mesh_terms: D000328:Adult; D000368:Aged; D015496:CD4-Positive T-Lymphocytes; D018414:CD8-Positive T-Lymphocytes; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D019410:Interleukin-16 / Q000032:analysis*; D018655:Lymphocyte Count; D008297:Male; D008875:Middle Aged; D012907:Smoking / Q000276:immunology / Q000378:metabolism*
chemical_list: D019410:Interleukin-16