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Cytotoxic effects of anthrax lethal toxin on macrophage-like cell line J774A.1
1Institute of Preventive Medicine, National Defense Medical Center, P. O. Box 90048-700, Taipei, Taiwan, ROC.
Abstract:
The cytotoxic effects of anthrax lethal toxin purified from an avirulent strain were examined on mouse macrophage-like J774A.1 cells. Cell death induced by high concentration of purified lethal toxin had the characteristics of necrosis. At lower concentrations, the toxin caused no morphological change and most of the cells were viable. Interestingly, apoptotic cells were observed when the cells were preincubated with a serine/threonine phosphatase inhibitor, calyculin A, and then exposed to a toxin concentration of 0.1 microg/ml. This is the first report that lethal toxin of the anthrax bacillus can induce both necrosis and apoptosis and that protein phosphatases are implicated in the regulation of bacterial toxin-induced apoptosis.
Insights
Anthrax lethal toxin induces necrosis at high concentrations. However, it triggers apoptosis in macrophage cells when combined with a phosphatase inhibitor, revealing a new mechanism of bacterial toxin-induced cell death.
Area of Science:
- Cell Biology
- Immunology
- Microbiology
Background:
- Anthrax lethal toxin (LT) is a key virulence factor of Bacillus anthracis.
- LT's cytotoxic effects on immune cells are not fully understood, particularly regarding cell death pathways.
Purpose of the Study:
- To investigate the cytotoxic effects of anthrax lethal toxin on mouse macrophage-like J774A.1 cells.
- To determine if LT can induce apoptosis and identify regulatory factors involved.
Main Methods:
- Exposure of J774A.1 cells to purified anthrax lethal toxin at varying concentrations.
- Preincubation with calyculin A, a serine/threonine phosphatase inhibitor, followed by LT exposure.
- Morphological assessment of cell death (necrosis vs. apoptosis).
Main Results:
- High concentrations of LT induced necrosis in J774A.1 cells.
- Low concentrations of LT did not cause significant cell death.
- Co-incubation with calyculin A and LT induced apoptotic cell death.
- This study is the first to show LT can induce both necrosis and apoptosis.
Conclusions:
- Anthrax lethal toxin can induce both necrotic and apoptotic cell death pathways in macrophages.
- Protein phosphatases play a regulatory role in bacterial toxin-induced apoptosis.
- These findings offer new insights into anthrax pathogenesis and host-pathogen interactions.