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Tumor necrosis factor alpha and interleukin 1 alpha enhance lipopolysaccharide-mediated bovine endothelial cell
S A Sharma1, T W Olchowy, Z Yang
1Department of Pathobiology, College of Veterinary Medicine, University of Tennessee, Knoxville.
Abstract:
Alveolar macrophages (AMs) are important in the host response to aerogenous pulmonary bacterial infections, such as Pasteurella haemolytica-induced pneumonia in cattle. Previous work has shown that AMs enhance P. haemolytica-mediated pulmonary endothelial cell (EC) damage in vitro. The purpose of this study was to determine the mechanism of AM-enhanced EC damage using an in vitro AM-EC coculture system consisting of AMs cultured on culture plate insert membranes and ECs in the underlying chamber. The addition of lipopolysaccharide (LPS) to the culture plate insert chamber resulted in EC damage indicated by 51Cr release, which was enhanced in the presence of AMs. To determine the role of AM-secreted cytokines, recombinant human interleukin 1 alpha (IL-1) or tumor necrosis factor alpha (TNF) was added to ECs simultaneously with varying concentrations of LPS. Although TNF and IL-1 alone had only marginal toxic effects on ECs, the simultaneous treatment of TNF or IL-1 with LPS greatly increased the LPS cytotoxic effect on ECs. In addition, IL-1 receptor antagonist eliminated the IL-1 enhancement of LPS-mediated EC toxicity. These results suggest that macrophage-secreted cytokines synergistically enhance LPS-mediated pulmonary EC damage.
Insights
Alveolar macrophages (AMs) enhance lung endothelial cell damage during bacterial infections. Macrophage-secreted cytokines, like IL-1 and TNF, synergize with lipopolysaccharide (LPS) to increase this damage.
Area of Science:
- Pulmonary immunology
- Cellular pathology
- Bacterial infection mechanisms
Background:
- Alveolar macrophages (AMs) play a crucial role in host defense against airborne bacterial pathogens.
- Previous studies indicate AMs exacerbate Pasteurella haemolytica-induced pulmonary endothelial cell (EC) damage.
- Understanding the mechanisms of this enhancement is vital for treating bovine pneumonia.
Purpose of the Study:
- To elucidate the mechanism by which AMs enhance EC damage in vitro.
- To investigate the role of AM-secreted cytokines in LPS-mediated EC injury.
- To establish an in vitro model for studying AM-EC interactions.
Main Methods:
- Utilized an in vitro AM-EC coculture system with AMs on inserts and ECs in the lower chamber.
- Induced EC damage using lipopolysaccharide (LPS) and measured 51Cr release.
- Administered recombinant human interleukin-1 alpha (IL-1) or tumor necrosis factor alpha (TNF) with LPS to ECs.
- Tested the effect of IL-1 receptor antagonist on LPS-mediated EC toxicity.
Main Results:
- LPS induced EC damage, which was significantly enhanced by the presence of AMs.
- Simultaneous treatment with IL-1 or TNF and LPS markedly increased EC cytotoxicity compared to LPS alone.
- IL-1-mediated enhancement of LPS toxicity was abolished by IL-1 receptor antagonist.
- TNF and IL-1 alone exhibited minimal toxic effects on ECs.
Conclusions:
- Macrophage-derived cytokines, specifically IL-1 and TNF, synergistically amplify LPS-induced pulmonary EC damage.
- This synergistic action of cytokines is a key mechanism in AM-enhanced EC injury during bacterial pneumonia.
- Targeting these cytokine pathways could offer therapeutic strategies for bacterial lung infections.