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Legionella pneumophila Outer Membrane Vesicles: Isolation and Analysis of Their Pro-inflammatory Potential on Macrophages
Published on: February 22, 2017
Tumor necrosis factor induces resistance of macrophages to Legionella pneumophila infection
S L McHugh1, C A Newton, Y Yamamoto
1Department of Medical Microbiology and Immunology, University of South Florida College of Medicine, Tampa, Florida 33612, USA.
Abstract:
Legionella pneumophila is an ubiquitous opportunistic intracellular pathogen that replicates readily in thioglycollate-elicited peritoneal macrophages from genetically susceptible A/J mice. Treatment of macrophage cultures in vitro with tumor necrosis factor-alpha (TNF-alpha) induced resistance of the macrophages to infection by Legionella as compared with control macrophages treated with medium alone. Addition of small amounts of monoclonal antibody to TNF-alpha restored susceptibility of the macrophages. Furthermore, antibody to the proinflammatory cytokine interleukin-1 (IL-1) alpha/beta increased resistance, but recombinant IL-1 had little effect. Such decreased susceptibility to Legionella growth in anti-IL-1 antibody-treated cultures corresponded with enhanced levels of TNF-alpha in the supernatants of the treated cells. An antibody to another proinflammatory cytokine with known immunoregulatory properties (i.e., IL-6) had little or no effect on the ability of the macrophages to be infected by Legionella and, furthermore, treatment with recombinant IL-6, similar to recombinant IL-1, did not modify the ability of the cells to be infected in vitro. These results indicate that TNF-alpha is important in controlling L. pneumophila replication, and IL-1 can regulate TNF-alpha levels, affecting susceptibility of macrophages to infection with an intracellular opportunistic pathogen like Legionella.
Insights
Tumor necrosis factor-alpha (TNF-alpha) enhances macrophage resistance to Legionella pneumophila infection. Interleukin-1 (IL-1) regulates TNF-alpha, influencing macrophage susceptibility to this opportunistic pathogen.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Legionella pneumophila is an opportunistic intracellular pathogen.
- Macrophages are key immune cells involved in controlling bacterial infections.
- Cytokines play crucial roles in regulating immune responses.
Purpose of the Study:
- To investigate the role of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) in macrophage susceptibility to Legionella pneumophila infection.
- To elucidate the regulatory relationship between IL-1 and TNF-alpha in controlling intracellular bacterial replication.
Main Methods:
- In vitro culture of thioglycollate-elicited peritoneal macrophages from A/J mice.
- Treatment of macrophages with recombinant cytokines (TNF-alpha, IL-1, IL-6) and monoclonal antibodies against these cytokines.
- Assessment of macrophage susceptibility to Legionella pneumophila infection by measuring bacterial replication.
- Quantification of cytokine levels in cell culture supernatants.
Main Results:
- Treatment with TNF-alpha induced macrophage resistance to L. pneumophila infection.
- Antibodies to TNF-alpha restored susceptibility, while antibodies to IL-1 increased resistance.
- IL-1 antibodies led to enhanced TNF-alpha levels, correlating with decreased bacterial growth.
- IL-6 had no significant effect on macrophage susceptibility to L. pneumophila.
Conclusions:
- TNF-alpha is a critical mediator in controlling Legionella pneumophila replication within macrophages.
- IL-1 modulates TNF-alpha production, thereby influencing macrophage susceptibility to intracellular opportunistic pathogens.
- These findings highlight the complex interplay of cytokines in host defense against bacterial infections.
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