title: Inhibition of natural killer cell cytotoxicity by interleukin-6: implications for the pathogenesis of macrophage activation syndrome.
abstract: OBJECTIVE
  Systemic juvenile idiopathic arthritis (JIA) is associated with high levels of interleukin-6 (IL-6) in the serum and synovial fluid, and impairment of natural killer (NK) cell function is often observed. This study was undertaken to evaluate a possible link between these 2 biologic findings and whether they may be associated with the development of macrophage activation syndrome, a condition frequently observed in systemic JIA.
  
  
  METHODS
  Splenocytes from wild-type (WT) or IL-6-transgenic (Tg) mice were evaluated for NK cell cytotoxicity using a (51) Cr-release assay. Numbers of NK cells and expression of perforin, granzyme B, CD69, and CD107a were evaluated by flow cytometry. Human peripheral blood mononuclear cells (PBMCs) isolated from healthy donors were treated with IL-6 and cultured in the presence or absence of tocilizumab (TCZ), an IL-6 receptor blocker. Human polyclonal NK cells from healthy donor PBMCs were evaluated for cell cytotoxicity and expression of perforin, granzyme B, and CD107a. PBMCs harvested from patients with systemic JIA during periods of active or inactive disease were left untreated or treated with IL-6 in combination with soluble IL-6 receptor and analyzed for the expression of perforin and granzyme B.
  
  
  RESULTS
  Splenic NK cell cytotoxicity was reduced in IL-6-Tg mice compared to WT mice. Levels of CD69 and CD107a showed no significant differences, whereas expression of perforin and granzyme B was impaired in NK cells from IL-6-Tg mice. Exposure of human peripheral blood NK cells to IL-6 led to reduced expression of perforin and granzyme B. Culturing human polyclonal NK cells in the presence of TCZ significantly increased cell cytotoxicity, and also increased expression of perforin and granzyme B. In patients with systemic JIA, a reduction in IL-6 plasma levels during disease remission correlated with the rescue of perforin and granzyme B expression in NK cells from these patients.
  
  
  CONCLUSIONS
  In both mice and humans, IL-6 down-modulated the cytotoxic activity of NK cells. This decrease was associated with reduced perforin and granzyme B levels in the absence of altered granule exocytosis.
authors.affiliation: IRCCS Bambino Gesú Children's Hospital, Rome, Italy.
authors.forename: Loredana
authors.initials: L
authors.lastname: Cifaldi
authors.affiliation: IRCCS Bambino Gesú Children's Hospital, Rome, Italy.
authors.forename: Giusi
authors.initials: G
authors.lastname: Prencipe
authors.affiliation: IRCCS Bambino Gesú Children's Hospital, Rome, Italy.
authors.forename: Ivan
authors.initials: I
authors.lastname: Caiello
authors.affiliation: IRCCS Bambino Gesú Children's Hospital, Rome, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Bracaglia
authors.affiliation: IRCCS Bambino Gesú Children's Hospital, Rome, Italy, and University of Pavia, Pavia, Italy.
authors.forename: Franco
authors.initials: F
authors.lastname: Locatelli
authors.affiliation: IRCCS Bambino Gesú Children's Hospital, Rome, Italy.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: De Benedetti
authors.affiliation: IRCCS Bambino Gesú Children's Hospital and Sapienza University of Rome, Rome, Italy.
authors.forename: Raffaele
authors.initials: R
authors.lastname: Strippoli
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003602:Cytotoxicity, Immunologic / Q000502:physiology*; D053804:Granzymes / Q000235:genetics / Q000378:metabolism; D006801:Humans; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D007694:Killer Cells, Natural / Q000187:drug effects / Q000378:metabolism*; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D055501:Macrophage Activation Syndrome / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D054353:Perforin / Q000235:genetics / Q000378:metabolism
chemical_list: D015850:Interleukin-6; D054353:Perforin; D053804:Granzymes