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Effects of ion composition and tonicity on human neutrophil antibacterial activity
1Cystic Fibrosis/Pulmonary Research and Treatment Center, Division of Pulmonary Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7248, USA. MWV@med.unc.edu
Insights
Altered airway surface liquids in cystic fibrosis (CF) do not impair neutrophil bacterial killing. Neutrophil function against Pseudomonas aeruginosa and Staphylococcus aureus remains effective despite changes in ionic composition and osmolarity in CF lungs.
Area of Science:
- Pulmonary Medicine
- Immunology
- Microbiology
Background:
- Infants with cystic fibrosis (CF) frequently develop Staphylococcus aureus infections, followed by Pseudomonas aeruginosa colonization.
- Despite robust neutrophil responses, CF patients often fail to clear P. aeruginosa pulmonary infections.
- Peripheral blood neutrophils from CF patients exhibit normal functions, suggesting an issue within the CF lung environment.
Purpose of the Study:
- To investigate if altered airway surface liquid (ASL) ionic composition in CF impairs neutrophil bactericidal activity.
- To determine the impact of varying ASL osmolarity and ionic concentrations on neutrophil killing of P. aeruginosa and S. aureus.
Main Methods:
- Human peripheral blood neutrophils were tested against P. aeruginosa and S. aureus in buffers with altered ionic composition and osmolarity.
- Neutrophil bactericidal activity was assessed in isotonic and +/- 50% deviated osmolar buffers.
- Superoxide production and enzyme secretion were measured in response to N-formylmethionylleucylphenylalanine.
Main Results:
- Neutrophil bacterial killing activity against P. aeruginosa and S. aureus was not reduced in isotonic buffers with varied ionic compositions (choline Cl, KCl, N-methyl-D-glucamine chloride).
- Amiloride and benzamil did not affect neutrophil killing function.
- Deviations from isotonicity by +/- 50% did not significantly diminish neutrophil bactericidal activity.
- Superoxide production and enzyme secretion were sensitive to the ionic milieu.
Conclusions:
- Postulated alterations in ASL ionic composition in CF lungs are insufficient to explain neutrophil failure in clearing P. aeruginosa infections.
- Neutrophil bactericidal capacity against common CF pathogens is maintained under simulated CF ASL conditions.
Abstract:
Infants with cystic fibrosis (CF) often are infected with Staphylococcus aureus (S. aur.), which is followed by colonization with Pseudomonas aeruginosa (P. aerug.). In spite of an excessive, neutrophil-dominated inflammatory response in the respiratory tract, patients with CF often succumb to pulmonary infections with P. aerug. Because peripheral blood neutrophils of these patients have normal functions, we examined whether hypothesized alterations of the airway surface liquids (ASL) in these patients significantly impair neutrophil bactericidal activity in the microenvironment of the CF lung. The ionic composition of CF ASL is still not entirely defined and has been speculated to be abnormally high or abnormally low in Na+ and Cl- concentrations; estimates of osmolarities have ranged from 200 (hypo-osmolar) to 285 (iso-osmolar) to > 300 meq/L (hyper-osmolar). Our data indicate that bacterial killing activity of human peripheral blood neutrophils against P. aerug. or S. aur. is not decreased in buffers in which NaCl was replaced with equimolar concentrations of choline Cl, KCl, or N-methyl-D-glucamine chloride to maintain isotonicity. Amiloride or benzamil, known modulators of Na+ transport in neutrophils, did not interfere with this neutrophil function. Deviations from isotonicity of +/- 50% also failed to diminish bactericidal activity of neutrophils significantly. In contrast, superoxide production and enzyme secretion in response to the chemotactic peptide N-formylmethionylleucylphenylalanine appeared to be sensitive to the ionic milieu of the assay buffers. Our results suggest that the postulated alterations in the ionic composition of ASL in CF lungs are insufficient to explain why neutrophils fail to clear infections with P. aerug. in these patients.