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Polymorphonuclear leukocyte- and Pseudomonas aeruginosa-induced damage to a human pulmonary epithelial cell line
1Department of Internal Medicine, Northwestern University Medical School, Chicago, IL 60611.
Abstract:
Polymorphonuclear leukocytes (PMNL) or Pseudomonas aeruginosa can damage the lung, but the manner in which they interact to induce toxicity is unclear. An in vitro model of the pulmonary epithelium was used to investigate interactions of PMNL and P. aeruginosa on epithelial cytotoxicity. A low inoculum of P. aeruginosa (10(7) bacteria) was minimally toxic to the epithelial cells (lysis = 9.0 +/- 2.9, detachment = 3.5 +/- 1.4). The addition of PMNL to the low inoculum markedly increased damage to the epithelial cells (lysis = 18.1 +/- 3.9, detachment = 17.6 +/- 3.6). Both the bacterium and a low-molecular-weight exoproduct were able to induce PMNL-mediated damage to epithelial cells. The damage was inhibited by serum or the addition of alpha 1 antiprotease but not by antioxidants. A larger inoculum of P. aeruginosa (10(9) bacteria) was directly toxic to the pulmonary cells (lysis = 44.8 +/- 4.1, detachment = 7.6 +/- 0.7). The damage was mediated by a heat-labile bacterial exoproduct. Pulmonary epithelial damage following pseudomonal infections may be related to either neutrophil or bacterial activity depending on the bacterial inoculum.
Insights
Polymorphonuclear leukocytes (PMNL) and Pseudomonas aeruginosa can harm lungs. Their interaction, especially with low bacterial doses, significantly increases lung cell damage, influenced by bacterial load.
Area of Science:
- Pulmonary medicine
- Microbiology
- Immunology
Background:
- Lung damage can result from polymorphonuclear leukocytes (PMNL) or Pseudomonas aeruginosa infections.
- The precise mechanisms of interaction and resulting epithelial cytotoxicity remain unclear.
Purpose of the Study:
- To investigate the synergistic or individual roles of PMNL and P. aeruginosa in causing pulmonary epithelial damage.
- To elucidate the factors influencing cytotoxicity based on bacterial inoculum size.
Main Methods:
- Utilized an in vitro model of the pulmonary epithelium.
- Exposed epithelial cells to varying concentrations of P. aeruginosa (10^7 and 10^9 bacteria/mL) with and without PMNL.
- Assessed epithelial cell lysis and detachment as indicators of cytotoxicity.
Main Results:
- A low P. aeruginosa inoculum (10^7) showed minimal direct toxicity, but its combination with PMNL significantly increased epithelial cell lysis and detachment.
- PMNL-mediated damage was induced by both the bacteria and a low-molecular-weight exoproduct, inhibited by serum or alpha 1 antiprotease.
- A high P. aeruginosa inoculum (10^9) caused direct, significant epithelial damage mediated by a heat-labile bacterial exoproduct.
Conclusions:
- Pulmonary epithelial damage in P. aeruginosa infections is dependent on the bacterial inoculum size.
- Low bacterial loads may lead to significant lung injury primarily through PMNL activation.
- High bacterial loads cause direct epithelial damage via bacterial factors, irrespective of PMNL presence.