title: Increased levels of the high mobility group box 1 protein sustain the inflammatory bone marrow microenvironment in patients with chronic idiopathic neutropenia via activation of toll-like receptor 4.
abstract: OBJECTIVE
  Chronic idiopathic neutropenia (CIN) is a granulocytic disorder characterized by increased apoptosis of the bone marrow (BM) granulocytic progenitor cells and an inflammatory BM microenvironment. The aim of this study was to investigate the possible involvement of Toll-like receptors (TLRs) in the production of pro-inflammatory mediators in CIN BM.
  
  
  METHODS
  We evaluated the expression of TLRs in patient BM cell subsets and adherent cells of long-term BM cultures (LTBMCs) using flow cytometry. We also examined the activation of TLR-mediated signaling using real-time PCR arrays and explored for potential endogenous TLR-specific ligands in CIN BM.
  
  
  RESULTS
  CIN patients (n = 30) displayed significantly increased expression of surface TLR4 in monocytes of BM and LTBMC adherent cells compared to controls (n = 27). The TLR signaling gene array study in purified BM CD14(+) cells showed that numerous TLR-related genes displayed at least two-fold increase in patients compared to controls. Among the over-expressed genes were genes related to the MyD88-dependent and MyD88-independent pathway suggesting a TLR4-mediated signaling. BM plasma from CIN patients induced the production of pro-inflammatory mediators including interleukin (IL)-6, IL-1β, tumor necrosis factor-α, and IL-8 by autologous BM monocytes, and this effect was abrogated by a specific TLR4 inhibitor. The levels of the high mobility group box 1 protein (HMGB1), representing a TLR4 ligand, were significantly increased in patient LTBMC supernatants compared to controls.
  
  
  CONCLUSIONS
  These data demonstrate a significant role of BM monocytes in the pathophysiology of CIN through the production of pro-inflammatory cytokines in a TLR4-mediated mechanism under the influence of endogenous ligands such as HMGB1.
authors: Department of Hematology, University of Crete School of Medicine, Heraklion, Greece.
authors: Maria
authors: M
authors: Velegraki
authors: Helen
authors: H
authors: Koutala
authors: Christos
authors: C
authors: Tsatsanis
authors: Helen A
authors: HA
authors: Papadaki
mesh_terms: D000328:Adult; D000368:Aged; D001853:Bone Marrow / Q000378:metabolism* / Q000473:pathology*; D016022:Case-Control Studies; D018929:Cell Culture Techniques; D060833:Cellular Microenvironment; D016207:Cytokines / Q000096:biosynthesis; D005260:Female; D015870:Gene Expression; D024243:HMGB1 Protein / Q000378:metabolism*; D006801:Humans; D007249:Inflammation / Q000378:metabolism*; D007958:Leukocyte Count; D018950:Lipopolysaccharide Receptors / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009000:Monocytes / Q000378:metabolism; D009503:Neutropenia / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*; D055815:Young Adult
chemical_list: D016207:Cytokines; D024243:HMGB1 Protein; D018950:Lipopolysaccharide Receptors; D051197:Toll-Like Receptor 4