title: Direct and indirect bacterial killing functions of neutrophil defensins in lung explants.
abstract: Studies of the antimicrobial activity of neutrophil defensins have mostly been carried out in microbiological media, and their effects on the host defense in physiological conditions are unclear. We examined 1) the antibacterial activity of defensins in physiological media with and without lung tissue present, 2) the effect of defensins on hydrogen peroxide (H(2)O(2)) production by lung tissue that had been exposed to bacteria, and 3) the effect of diphenyleneiodonium (DPI), an inhibitor of reactive oxygen species formation, on the antibacterial activity of defensins in the presence of lung tissue. Defensins were incubated with Escherichia coli or Pseudomonas aeruginosa in the absence or presence of primary cultured mouse lung explants. Defensins reduced bacterial counts by approximately 65-fold and approximately 25-fold, respectively, at 48 h; bacterial counts were further decreased by approximately 600-fold and approximately 12,000-fold, respectively, in the presence of lung tissue. Defensins induced H(2)O(2) production by lung tissue, and the rate of killing of E. coli by defensins was reduced by approximately 2,500-fold in the presence of 10 microM DPI. We conclude that defensins exert a significant antimicrobial effect under physiological conditions and that this effect is enhanced in the presence of lung tissue by a mechanism that involves the production of reactive oxygen species.
authors.affiliation: Respiratory Division, Department of Anaesthesia, St. Michael's Hospital, Toronto M5B 1W8, Canada.
authors.forename: G A
authors.initials: GA
authors.lastname: Porro
authors.forename: J H
authors.initials: JH
authors.lastname: Lee
authors.forename: J
authors.initials: J
authors.lastname: de Azavedo
authors.forename: I
authors.initials: I
authors.lastname: Crandall
authors.forename: T
authors.initials: T
authors.lastname: Whitehead
authors.forename: E
authors.initials: E
authors.lastname: Tullis
authors.forename: T
authors.initials: T
authors.lastname: Ganz
authors.forename: M
authors.initials: M
authors.lastname: Liu
authors.forename: A S
authors.initials: AS
authors.lastname: Slutsky
authors.forename: H
authors.initials: H
authors.lastname: Zhang
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D015169:Colony Count, Microbial; D046508:Culture Techniques; D003550:Cystic Fibrosis / Q000378:metabolism; D023082:Defensins / Q000302:isolation & purification / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000502:physiology; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008070:Lipopolysaccharides / Q000378:metabolism; D008168:Lung / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009504:Neutrophils / Q000276:immunology* / Q000378:metabolism; D009861:Onium Compounds / Q000494:pharmacology; D016877:Oxidants / Q000096:biosynthesis; D011550:Pseudomonas aeruginosa / Q000502:physiology
chemical_list: D000900:Anti-Bacterial Agents; D023082:Defensins; D004791:Enzyme Inhibitors; D008070:Lipopolysaccharides; D009861:Onium Compounds; D016877:Oxidants; C007517:diphenyleneiodonium; D006861:Hydrogen Peroxide; D007770:L-Lactate Dehydrogenase