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Harvesting Murine Alveolar Macrophages and Evaluating Cellular Activation Induced by Polyanhydride Nanoparticles
Published on: June 8, 2012
The effects of cyclosporine and dexamethasone on an alveolar macrophage cell line (NR8383)
H A Hidalgo1, R J Helmke, V F German
1Department of Pediatrics, University of Texas Health Science Center, San Antonio 78284.
Abstract:
Lung infections are a major source of morbidity and mortality in recipients of lung transplants. Prominent among the pathogens that cause pneumonias in these subjects are gram-negative bacilli, particularly Pseudomonas strains. One important reason that bacteria infect the lungs of these patients is that pulmonary defenses are impaired by the drugs used to prevent transplant rejection. Using a rat alveolar macrophage cell line (NR8383), we measured the effects of exposure (24 hr) to cyclosporine and dexamethasone (DEX) on the ability of these cells to (1) kill Pseudomonas aeruginosa (Pa); (2) produce H2O2; and (3) release tumor necrosis factor. We found that the bactericidal activity against unopsonized or opsonized Pa of NR8383 cells was unaltered by CsA (0.1, 0.5, or 1 micrograms/ml), DEX (10(-6) M), or CsA + DEX (0.5 micrograms/ml + 10(-6) M, respectively). Likewise, LPS-induced TNF release, and zymosan A and Pa-induced H2O2 production were unaltered by CsA (0.1 or 1 microgram/ml). In contrast, H2O2 production and TNF release were decreased by about 50% and 90%, respectively, by DEX exposure (10(-6) M). Thus, while DEX but not CsA decreased TNF release and H2O2 production in NR8383 cells, bactericidal activity against Pa was unaffected. One explanation for these results is that decreases in TNF or H2O2 of the magnitude we observed do not impair bactericidal activity against Pa; however, an alternative explanation is that Pa are killed by NR8383 cells through other mechanisms. Interpretation of these results must take into consideration the fact that macrophages from different species and tissues may respond differently to various stimuli.
Insights
Lung transplant patients face infections from Pseudomonas aeruginosa. While dexamethasone (DEX) reduced macrophage H2O2 and TNF release, neither DEX nor cyclosporine (CsA) affected bacterial killing, suggesting alternative defense mechanisms against Pseudomonas aeruginosa.
Area of Science:
- Immunology
- Transplantation Medicine
- Microbiology
Background:
- Lung transplant recipients are susceptible to infections, particularly Gram-negative bacilli like Pseudomonas aeruginosa.
- Immunosuppressive drugs, such as cyclosporine (CsA) and dexamethasone (DEX), used to prevent transplant rejection, can impair pulmonary defenses.
- Alveolar macrophages play a crucial role in lung immunity, but their function may be altered by immunosuppression.
Purpose of the Study:
- To investigate the impact of CsA and DEX on the function of rat alveolar macrophages (NR8383 cell line).
- To assess the effects of these immunosuppressants on macrophage-mediated killing of Pseudomonas aeruginosa (Pa).
- To evaluate the influence of CsA and DEX on hydrogen peroxide (H2O2) production and tumor necrosis factor (TNF) release by macrophages.
Main Methods:
- A rat alveolar macrophage cell line (NR8383) was exposed to varying concentrations of CsA and DEX for 24 hours.
- Macrophage bactericidal activity against opsonized and unopsonized Pseudomonas aeruginosa was measured.
- Hydrogen peroxide (H2O2) production (induced by zymosan A and Pa) and tumor necrosis factor (TNF) release (induced by LPS) were quantified.
Main Results:
- Neither CsA nor DEX, alone or in combination, significantly altered the bactericidal activity of NR8383 cells against Pseudomonas aeruginosa.
- CsA did not affect LPS-induced TNF release or zymosan A and Pa-induced H2O2 production.
- DEX significantly decreased H2O2 production by approximately 50% and TNF release by about 90% in NR8383 cells.
Conclusions:
- Dexamethasone, but not cyclosporine, impairs key macrophage functions (H2O2 and TNF production) in vitro.
- Despite reduced H2O2 and TNF production, macrophage bactericidal activity against Pseudomonas aeruginosa remained unaffected.
- These findings suggest that other mechanisms may contribute to Pseudomonas aeruginosa clearance by macrophages, or that the observed reductions are insufficient to impair bacterial killing in this model.
