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Pulmonary intravascular monocytes/macrophages in a rat model of sepsis
Chandrashekhar Charavaryamath1, Kyathanahalli S Janardhan, Sarah Caldwell
1Immunology Research Group and Department of Veterinary Biomedical Sciences, University of Saskatchewan, Saskatoon, Canada.
Abstract:
Sepsis induces recruitment of neutrophils and monocytes/macrophages in the lung and enhances host susceptibility to a secondary bacterial challenge. The phenotype and functions of recruited pulmonary intravascular monocytes/macrophages (PIMMs) in sepsis remain largely unknown. Therefore, we characterized PIMM recruitment and functions in a rat model of E. coli-induced sepsis. Male Sprague-Dawley rats were injected intraperitoneally with saline (n=10) and 48 hr after the saline treatment treated intravenously with either saline (n=5) or E. coli lipopolysachharide (LPS; 1.5 microg/kg body weight; n=5). A second group of 10 rats was infected intraperitoneally with E. coli (2x10(7) CFU/100 g) followed by intravenous injection of either saline (n=5) or LPS (n=5) 48 hr after the first treatment. Rats were euthanized at 6 hr after LPS treatment. Immunocytochemistry showed more PIMMs stained with ED-1 antibody, which specifically reacts with rat monocytes/macrophages, in rats infected with E. coli compared with the controls (P<0.05). LPS treatment of E. coli-infected rats increased the numbers of PIMMs (P<0.05) and induced more inflammation compared to other groups. Immuno-electron microscopy localized TNF-alpha, IL-10, and TGF-beta2 in recruited PIMMs in rats challenged with both E. coli and LPS. ELISA on lung homogenates showed higher concentrations of TNF-alpha, IL-10, and TGF-beta2 in rats treated with both E. coli and LPS compared with those treated with only LPS or E. coli (P<0.05). We conclude that ED-1-positive PIMMs are recruited in this model of sepsis and contain TNF-alpha, IL-10, and TGF-beta2.
Insights
Sepsis recruits monocytes/macrophages to the lungs, influencing immune responses. These pulmonary intravascular monocytes/macrophages (PIMMs) in sepsis contain key inflammatory and anti-inflammatory cytokines.
Area of Science:
- Immunology
- Cell Biology
- Pathophysiology
Background:
- Sepsis leads to immune cell infiltration in the lungs, increasing susceptibility to secondary infections.
- The characteristics and roles of pulmonary intravascular monocytes/macrophages (PIMMs) during sepsis are not well understood.
Purpose of the Study:
- To investigate the recruitment and function of PIMMs in a rat model of sepsis.
- To identify the cytokine content within recruited PIMMs.
Main Methods:
- Established an Escherichia coli (E. coli)-induced sepsis model in Sprague-Dawley rats.
- Utilized immunocytochemistry (ED-1 antibody) and immuno-electron microscopy to identify and localize PIMMs and cytokines.
- Quantified cytokine levels (TNF-alpha, IL-10, TGF-beta2) using ELISA.
Main Results:
- E. coli infection significantly increased PIMM recruitment compared to controls.
- Lipopolysaccharide (LPS) treatment in infected rats further elevated PIMM numbers and induced greater inflammation.
- Recruited PIMMs in E. coli and LPS-treated rats contained TNF-alpha, IL-10, and TGF-beta2.
- Lung homogenates from dual-treated rats showed elevated levels of these cytokines.
Conclusions:
- ED-1-positive PIMMs are recruited during E. coli-induced sepsis in rats.
- These PIMMs are a source of TNF-alpha, IL-10, and TGF-beta2, suggesting a role in modulating the inflammatory response during sepsis.
