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Lethal toxin actions and their consequences
1Departments of Microbiology and Immunology, Duke University Medical Center, Durham, NC 27710, USA. hanna@abacus.mc.duke.edu
Abstract:
After entry of infectious anthrax spores into the body, host-specific signals induce spore germination, outgrowth of vegetative bacilli and the expression of lethal toxin and other virulence factors. Anthrax lethal toxin (LeTx) is a virulence factor responsible for the major pathologies seen during systemic anthrax infections. Injection of sterile LeTx into test animals mimics the shock and sudden death seen during active bacterial infections. Once large levels of LeTx are produced within the body, destruction of bacteria by administration of antibiotics is usually unsuccessful. The LeTx is believed to be secreted into the bloodstream where it circulates freely throughout the body and binds and enters host cells. Once in the cytoplasm, the lethal factor acts as a zinc-metalloprotease disrupting normal homoeostatic functions. Macrophages are a uniquely sensitive cell type that seem to be vital global mediators of toxin-induced pathologies. Removal of macrophages from mice renders them insensitive to LeTx challenge. Low levels of lethal toxin induce macrophage production, in vitro, of the shock-inducing cytokines TNF and Il-1beta. Higher levels of LeTx cause over-production of reactive oxygen intermediates, bursting of macrophages and release of mediators of shock. We believe that agents capable of blocking key steps of the lethal toxin cascade may prove useful in combating anthrax pathologies.
Insights
Anthrax lethal toxin (LeTx) causes severe pathologies by disrupting host cells, particularly macrophages. Blocking the LeTx cascade offers a potential therapeutic strategy against anthrax.
Area of Science:
- Microbiology
- Immunology
- Toxicology
Background:
- Anthrax lethal toxin (LeTx) is a key virulence factor in systemic anthrax infections.
- LeTx injection in animals mimics the shock and sudden death observed in active infections.
- Antibiotic treatment is often ineffective once high levels of LeTx are produced.
Purpose of the Study:
- To investigate the mechanisms by which anthrax lethal toxin induces pathologies.
- To identify host cells and pathways critically involved in LeTx-mediated disease.
- To explore potential therapeutic targets within the LeTx cascade.
Main Methods:
- Administration of sterile LeTx to test animals to observe pathological effects.
- Investigating the role of macrophages in LeTx-induced pathologies through their removal.
- In vitro studies assessing macrophage responses to varying LeTx concentrations, including cytokine production and reactive oxygen species.
Main Results:
- LeTx circulates in the bloodstream, enters host cells, and disrupts cellular functions as a zinc-metalloprotease.
- Macrophages are highly sensitive to LeTx and play a vital role in mediating toxin-induced pathologies.
- Low LeTx levels stimulate shock-inducing cytokine production (TNF, Il-1beta) by macrophages.
- High LeTx levels lead to macrophage overproduction of reactive oxygen intermediates, cell lysis, and shock mediators.
Conclusions:
- Anthrax lethal toxin is a potent mediator of systemic anthrax pathology.
- Macrophages are critical cellular targets and mediators of LeTx-induced shock and death.
- Targeting key steps in the LeTx cascade presents a promising therapeutic approach for anthrax.