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Eicosanoids produced during interactions between Pseudomonas aeruginosa and alveolar macrophages are
T C Sorrell1, C P Rochester, F N Breen
1University of Sydney Department of Medicine, NSW, Australia.
Abstract:
Eicosanoid production during phagocytosis of pyogenic bacteria by rabbit alveolar macrophages was studied as a model of early events in the pathogenesis of pneumonia. Adherent alveolar macrophages, prelabelled with [3H]-arachidonic acid (AA), were incubated with live, opsonized Staphylococcus aureus or Pseudomonas aeruginosa (bacteria:macrophage ratio of 50:1) at 37 degrees C for 90 min. Supernatant eicosanoids were extracted and separated by reverse phase high performance liquid chromatography (RP-HPLC). While the amounts of labelled PGE2, TXB2, and PGD2 produced in response to the two organisms were equal, the amount of PGF2 alpha elicited by S. aureus amounted to three times that released during macrophage challenge with P. aeruginosa. Overall, preferential release of cyclooxygenase products occurred during phagocytosis of S. aureus. In contrast, eicosanoids identified presumptively as oxygenated metabolites of AA predominated in cultures challenged with opsonized P. aeruginosa. Live, non-opsonized P. aeruginosa elicited the same profile of eicosanoids, but in reduced amounts. Inhibitor studies indicated that these AA derivatives were not synthesized via the macrophage lipoxygenase pathway. Their production was dependent on the viability of P. aeruginosa. Macrophages challenged with opsonized, heat-killed P. aeruginosa resulted in production of an eicosanoid profile similar to that elicited by S. aureus. Secondary metabolism by P. aeruginosa of eicosanoids released from the macrophage did not contribute to the unique profile produced during the interaction of this organism with labelled macrophages. Our data indicate that during binding to macrophages, the primary human pathogen, P. aeruginosa, specifically modulates the profile of eicosanoids produced. This effect on inflammatory mediators may be of biological significance in the pathogenesis of pneumonia.
Insights
Pseudomonas aeruginosa alters eicosanoid production by macrophages during pneumonia pathogenesis. This modulation of inflammatory mediators by P. aeruginosa is critical for understanding pneumonia development.
Area of Science:
- Immunology
- Pathogenesis
- Cellular Biology
Background:
- Pneumonia pathogenesis involves early inflammatory events.
- Eicosanoid production by macrophages plays a key role in inflammation.
Purpose of the Study:
- To investigate eicosanoid production during phagocytosis of pyogenic bacteria by rabbit alveolar macrophages.
- To model early events in pneumonia pathogenesis.
Main Methods:
- Rabbit alveolar macrophages were labeled with [3H]-arachidonic acid (AA).
- Macrophages were incubated with Staphylococcus aureus or Pseudomonas aeruginosa.
- Eicosanoids were extracted and analyzed using reverse-phase high-performance liquid chromatography (RP-HPLC).
Main Results:
- S. aureus elicited higher levels of PGF2 alpha compared to P. aeruginosa.
- Phagocytosis of S. aureus led to preferential release of cyclooxygenase products.
- P. aeruginosa challenge resulted in predominant oxygenated AA metabolites, dependent on bacterial viability.
- Heat-killed P. aeruginosa induced an eicosanoid profile similar to S. aureus.
Conclusions:
- P. aeruginosa specifically modulates macrophage eicosanoid profiles during binding.
- This modulation of inflammatory mediators by P. aeruginosa is significant in pneumonia pathogenesis.
- Eicosanoid profiles differ based on the specific bacterial pathogen and its viability.