title: Immunohistological expression of interleukin 16 in human tonsils.
abstract: BACKGROUND
  Interleukin 16 (IL-16) acts highly chemotactic on CD4-bearing cells. Besides chemotaxis, IL-16 has numerous immunomodulatory effects, and not only on T cells.
  
  
  OBJECTIVE
  To determine IL-16 expression in human tonsils.
  
  
  METHODS
  Tonsillar follicles were immunohistologically characterized to elicit a possible cellular source of IL-16 expression.
  
  
  RESULTS
  The mantle zone of immature and mature B cells was CD22 immunoreactive (ir), whereas the germinal center of activated B cells was CD23-ir. Plasma cells that were CD38-ir were observed extrafollicularly beneath the epithelium and within the germinal center. T cells were found most frequently in the extrafollicular space, with a majority of CD4 cells. CD68-ir macrophages were predominantly found within the germinal center. Immunostaining of anti-IL-16 revealed strong cytoplasmatic reactivity of extrafollicular cells and of cells at the outer rim of the mantle zone. Numerous cells adherent to the stratified squamous epithelium were IL-16-ir as well. Double immunostaining identified CD4(+) T cells as the major cellular source of IL-16 expression. Furthermore, a population of CD22(+) B cells at the outer rim of the mantle zone expressed IL-16 as well.
  
  
  CONCLUSIONS
  Interleukin 16 was mainly expressed in a typical CD4-like pattern in human tonsils. Our data strongly suggest that CD4(+) lymphocytes constitute the major cellular source for IL-16. We hypothesize that the double-immunostained CD4-ir and IL-16-ir cells represent activated T cells. Because CD22(+) B cells at the outer rim of the mantle zone expressed IL-16 as well, we conclude that this area might constitute the locus of IL-16-mediated B-cell differentiation.
authors.affiliation: Department of Oto-Rhino-Laryngology/Head and Neck Surgery, Ludwig-Maximilians-University, Klinikum Grosshadern, Marchioninistr.15, 81377 Munich, Germany. mkramer@hno.med.uni-muenchen.de
authors.forename: M F
authors.initials: MF
authors.lastname: Kramer
authors.forename: B
authors.initials: B
authors.lastname: Mack
authors.forename: G
authors.initials: G
authors.lastname: Rasp
mesh_terms: D002648:Child; D006801:Humans; D007150:Immunohistochemistry; D019410:Interleukin-16 / Q000032:analysis / Q000096:biosynthesis*; D014066:Palatine Tonsil / Q000737:chemistry / Q000276:immunology* / Q000473:pathology
chemical_list: D019410:Interleukin-16