title: Antimicrobial peptides are highly abundant and active in postoperative pleural drainage fluids.
abstract: BACKGROUND
  The human lung is considered a nonsterile organ, and surgical interventions therefore take place in a more or less contaminated operating field. Nevertheless, infectious complications of the pleural cavity are low after major lung resections. Antimicrobial peptides (AMPs) are part of the innate immunity and display a broad capacity to kill pathogens. We hypothesized that the pleural space must have a high natural antimicrobial barrier and that AMPs might effectively protect the pleural cavity.
  
  
  METHODS
  Pleural effusions were collected after lung operations. Antimicrobial activity of the fluids against gram-positive and gram-negative pathogens was analyzed by microdilution assays. AMPs were determined by enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), and immunohistochemical analysis. The impact of proinflammatory triggers on AMP release from pleural mesothelial cells was evaluated.
  
  
  RESULTS
  Antimicrobial activity assays revealed high bactericidal properties of postoperative pleural drainage fluids. They effectively killed gram-negative pathogens (Escherichia coli, Pseudomonas aeruginosa) as well as gram-positive pathogens (Staphylococcus aureus, Streptococcus pneumoniae, and Streptococcus pyogenes). A variety of AMPs was detected at constantly high concentrations in the pleural fluids. They mainly derived from leukocytes and pleural epithelium. Although proinflammatory cytokine levels were elevated in the postoperative pleural fluids, AMP expression could not be augmented by Toll-like receptor (TLR) triggering or by the proinflammatory cytokines interleukin (IL)-1β and tumor necrosis factor (TNF)α.
  
  
  CONCLUSIONS
  We provide the first evidence of a high abundance of AMPs in postoperative pleural fluids. Our findings might explain the broad protection against infectious complications of the pleural space after major lung operations.
authors.affiliation: Department of Thoracic Surgery, Medical University Vienna, Austria.
authors.forename: Konrad
authors.initials: K
authors.lastname: Hoetzenecker
authors.affiliation: Department of Thoracic Surgery, Medical University Vienna, Austria.
authors.forename: Moritz
authors.initials: M
authors.lastname: Hochdaninger
authors.affiliation: Department of Thoracic Surgery, Medical University Vienna, Austria; Christian Doppler Laboratory for Cardiac and Thoracic Diagnosis and Regeneration, Medical University Vienna, Austria.
authors.forename: Denise
authors.initials: D
authors.lastname: Traxler
authors.affiliation: Department of Dermatology, Research Division of Biology and Pathobiology of the Skin, Medical University Vienna, Austria.
authors.forename: Maria
authors.initials: M
authors.lastname: Gschwandtner
authors.affiliation: Department of Thoracic Surgery, Medical University Vienna, Austria; Christian Doppler Laboratory for Cardiac and Thoracic Diagnosis and Regeneration, Medical University Vienna, Austria.
authors.forename: Mohammad Mahdi
authors.initials: MM
authors.lastname: Kasiri
authors.affiliation: Department of Thoracic Surgery, Medical University Vienna, Austria; Christian Doppler Laboratory for Cardiac and Thoracic Diagnosis and Regeneration, Medical University Vienna, Austria.
authors.forename: Andreas
authors.initials: A
authors.lastname: Mitterbauer
authors.affiliation: Department of Thoracic Surgery, Medical University Vienna, Austria; Christian Doppler Laboratory for Cardiac and Thoracic Diagnosis and Regeneration, Medical University Vienna, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Schweiger
authors.affiliation: Department of Thoracic Surgery, Medical University Vienna, Austria.
authors.forename: Balazs
authors.initials: B
authors.lastname: Hegedus
authors.affiliation: Department of Thoracic Surgery, Medical University Vienna, Austria.
authors.forename: Walter
authors.initials: W
authors.lastname: Klepetko
authors.affiliation: Department of Dermatology, Research Division of Biology and Pathobiology of the Skin, Medical University Vienna, Austria.
authors.forename: Erwin
authors.initials: E
authors.lastname: Tschachler
authors.affiliation: Department of Thoracic Surgery, Medical University Vienna, Austria; Christian Doppler Laboratory for Cardiac and Thoracic Diagnosis and Regeneration, Medical University Vienna, Austria. Electronic address: hendrik.ankersmit@meduniwien.ac.at.
authors.forename: Hendrik J
authors.initials: HJ
authors.lastname: Ankersmit
authors.affiliation: Department of Dermatology, Research Division of Biology and Pathobiology of the Skin, Medical University Vienna, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Mildner
mesh_terms: D001826:Body Fluids / Q000737:chemistry; D023082:Defensins / Q000032:analysis / Q000502:physiology*; D004322:Drainage; D006090:Gram-Negative Bacteria; D006801:Humans; D010994:Pleura / Q000276:immunology*; D011184:Postoperative Period
chemical_list: D023082:Defensins