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Characteristics of alveolar macrophages in experimental septic lung
1First Department of Surgery, Kyushu University Faculty of Medicine, Fukuoka, Japan.
Abstract:
We investigated the pathogenesis of lung injury in sepsis (septic adult respiratory distress syndrome) by focusing on the functional changes of alveolar macrophages (AMs). Sepsis was induced in male WK rats by cecal ligation and puncture. Histological examination of the lungs from this experimental model revealed edematous change at 24 h after the surgery. The protein and endotoxin concentrations in the bronchoalveolar lavage fluid (BALF) increased with time after the surgery. The time course studies of AM function after surgery indicated that AMs from septic rats were activated by endotoxins. Specifically, this was suggested by the finding that AM adherence to and spreading on a plastic dish had increased. On stimulation, these AMs enhanced generation of superoxide anions and increased release of lysosomal enzymes, such as beta-glucuronidase. On the other hand, AMs in sepsis generated much smaller amounts of arachidonate lipoxygenase metabolites, such as leukotriene B4 (LTB4) and 12- and 5-hydroxyeicosatetraenoic acids (HETEs), on stimulation than did AMs from sham rats or untreated rats. However, the concentrations of immunoreactive LTC4 in the BALF of septic rats seemed to be higher than in untreated rats. It is suggested that the AMs of septic rats released lipoxygenase metabolites in alveoli and that these AMs could not be stimulated in vitro. These functional changes in the AMs of septic rats progressed along with the sepsis. These results implicate AMs in the development and progression of septic lung injury by releasing superoxide anions, beta-glucuronidase, and arachidonate metabolites. Furthermore, we speculate that reduced production of LTB4 by septic AMs may increase host susceptibility to severe pulmonary infection during septic ARDS.
Insights
Alveolar macrophages (AMs) in sepsis-induced lung injury show altered function, releasing more damaging superoxide anions and enzymes. Reduced leukotriene B4 (LTB4) production by these AMs may increase susceptibility to pulmonary infections in septic adult respiratory distress syndrome (ARDS).
Area of Science:
- Immunology
- Pathophysiology
- Pulmonary Medicine
Background:
- Sepsis-induced lung injury, or septic adult respiratory distress syndrome (ARDS), involves complex inflammatory processes.
- Alveolar macrophages (AMs) play a critical role in the lung's immune response and are implicated in ARDS pathogenesis.
Purpose of the Study:
- To investigate the functional changes in alveolar macrophages (AMs) during the development of septic lung injury.
- To elucidate the role of AMs in the pathogenesis and progression of lung injury in a rat model of sepsis.
Main Methods:
- Sepsis was induced in rats using cecal ligation and puncture.
- Lung histology, bronchoalveolar lavage fluid (BALF) analysis, and functional assays of AMs were performed at various time points post-surgery.
- AM function was assessed by measuring adherence, spreading, superoxide anion generation, lysosomal enzyme release, and arachidonate metabolite production.
Main Results:
- Septic rats exhibited lung edema, increased protein and endotoxin in BALF, and activated AMs.
- Activated AMs showed increased adherence, spreading, superoxide anion generation, and beta-glucuronidase release.
- AMs from septic rats produced significantly less leukotriene B4 (LTB4) and hydroxyeicosatetraenoic acids (HETEs) but higher LTC4 in BALF compared to controls.
- Functional changes in AMs correlated with the progression of sepsis.
Conclusions:
- Alveolar macrophages are implicated in the development and progression of septic lung injury through the release of superoxide anions, beta-glucuronidase, and arachidonate metabolites.
- Reduced production of LTB4 by septic AMs may impair the host's defense against pulmonary infections during septic ARDS.
- These findings highlight AMs as key players in septic lung injury and suggest potential therapeutic targets.