title: Fibrocytes contribute to inflammation and fibrosis in chronic hypersensitivity pneumonitis through paracrine effects.
abstract: BACKGROUND
  Hypersensitivity pneumonitis (HP) represents a lung inflammation provoked by exposure to a variety of antigens. Chronic HP may evolve to lung fibrosis. Bone marrow-derived fibrocytes migrate to injured tissues and contribute to fibrogenesis, but their role in HP is unknown.
  
  
  OBJECTIVE
  To assess the possible participation of fibrocytes in chronic HP.
  
  
  METHODS
  CD45(+)/CXCR4(+)/Col-I(+) circulating fibrocytes were evaluated by flow cytometry, and the presence of fibrocytes in HP and normal lungs by confocal microscopy. The concentration of CXCL12 in plasma and bronchoalveolar lavage fluids was quantified by ELISA. The effect of fibrocytes on lung fibroblasts and T lymphocytes was examined in co-cultures.
  
  
  RESULTS
  The percentage of circulating fibrocytes was significantly increased in patients with HP compared with healthy individuals (5.3 ± 3.4% vs. 0.8 ± 0.7%; P = 0.00004). Numerous fibrocytes were found infiltrating the HP lungs near fibroblasts and lymphocytes. Plasma CXCL12 concentration was significantly increased in patients with HP (2,303.3 ± 813.7 vs. 1,385.6 ± 318.5 pg/ml; P = 0.00003), and similar results were found in bronchoalveolar lavage fluids. The chemokine was primarily expressed by epithelial cells. In co-cultures, fibrocytes induced on lung fibroblasts a significant increase in the expression of α1 type I collagen, matrix metalloprotease-1, and platelet-derived growth factor-β. Likewise, fibrocytes induced the up-regulation of CCL2 in HP lymphocytes and fibroblasts.
  
  
  CONCLUSIONS
  These findings demonstrate that high levels of fibrocytes are present in the peripheral blood of patients with chronic HP and that these cells infiltrate the HP lungs. Fibrocytes may participate in the pathogenesis of HP, amplifying the inflammatory and fibrotic response by paracrine signaling inducing the secretion of a variety of proinflammatory and profibrotic molecules.
authors.affiliation: 1 Instituto Nacional de Enfermedades Respiratorias Ismael Cosío Villegas, Mexico City, Mexico; and.
authors.forename: Carolina
authors.initials: C
authors.lastname: García de Alba
authors.forename: Ivette
authors.initials: I
authors.lastname: Buendia-Roldán
authors.forename: Alfonso
authors.initials: A
authors.lastname: Salgado
authors.forename: Carina
authors.initials: C
authors.lastname: Becerril
authors.forename: Remedios
authors.initials: R
authors.lastname: Ramírez
authors.forename: Yolanda
authors.initials: Y
authors.lastname: González
authors.forename: Marco
authors.initials: M
authors.lastname: Checa
authors.forename: Carmen
authors.initials: C
authors.lastname: Navarro
authors.forename: Victor
authors.initials: V
authors.lastname: Ruiz
authors.forename: Annie
authors.initials: A
authors.lastname: Pardo
authors.forename: Moisés
authors.initials: M
authors.lastname: Selman
mesh_terms: D000328:Adult; D000368:Aged; D000542:Alveolitis, Extrinsic Allergic / Q000378:metabolism / Q000473:pathology*; D015415:Biomarkers / Q000378:metabolism; D015153:Blotting, Western; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry; D016022:Case-Control Studies; D054377:Chemokine CXCL12 / Q000378:metabolism; D002908:Chronic Disease; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005347:Fibroblasts / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D017493:Leukocyte Common Antigens / Q000378:metabolism; D008297:Male; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D018613:Microscopy, Confocal; D008875:Middle Aged; D010446:Peptide Fragments / Q000378:metabolism; D011658:Pulmonary Fibrosis / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D060888:Real-Time Polymerase Chain Reaction; D019718:Receptors, CXCR4 / Q000378:metabolism
chemical_list: D015415:Biomarkers; C515255:CXCL12 protein, human; C527276:CXCR4 protein, human; D054377:Chemokine CXCL12; D010446:Peptide Fragments; D019718:Receptors, CXCR4; D017493:Leukocyte Common Antigens; C516769:PTPRC protein, human; C471083:Col-1 peptide, human; D020778:Matrix Metalloproteinase 2
keywords: chemokines; chronic hypersensitivity pneumonitis; circulating fibrocytes; paracrine; pulmonary fibrosis