Related Experiment Videos
Salmonella typhimurium invasion induces apoptosis in infected macrophages
D M Monack1, B Raupach, A E Hromockyj
1Department of Microbiology and Immunology, Stanford School of Medicine, Stanford University, CA 94305, USA.
Abstract:
Invasive Salmonella typhimurium induces dramatic cytoskeletal changes on the membrane surface of mammalian epithelial cells and RAW264.7 macrophages as part of its entry mechanism. Noninvasive S. typhimurium strains are unable to induce this membrane ruffling. Invasive S. typhimurium strains invade RAW264.7 macrophages in 2 h with 7- to 10-fold higher levels than noninvasive strains. Invasive S. typhimurium and Salmonella typhi, independent of their ability to replicate intracellularly, are cytotoxic to RAW264.7 macrophages and, to a greater degree, to murine bone marrow-derived macrophages. Here, we show that the macrophage cytotoxicity mediated by invasive Salmonella is apoptosis, as shown by nuclear morphology, cytoplasmic vacuolization, and host cell DNA fragmentation. S. typhimurium that enter cells causing ruffles but are mutant for subsequent intracellular replication also initiate host cell apoptosis. Mutant S. typhimurium that are incapable of inducing host cell membrane ruffling fail to induce apoptosis. The activation state of the macrophage plays a significant role in the response of macrophages to Salmonella invasion, perhaps indicating that the signal or receptor for initiating programmed cell death is upregulated in activated macrophages. The ability of Salmonella to promote apoptosis may be important for the initiation of infection, bacterial survival, and escape of the host immune response.
Insights
Invasive Salmonella typhimurium triggers host cell death through apoptosis, a process linked to membrane ruffling during bacterial entry. This programmed cell death is crucial for Salmonella infection and immune evasion.
Area of Science:
- Microbiology
- Cell Biology
- Immunology
Background:
- Salmonella typhimurium invasion involves cytoskeletal changes and membrane ruffling in host cells.
- Invasive Salmonella strains exhibit higher invasion rates and cytotoxicity compared to noninvasive strains.
Purpose of the Study:
- To investigate the mechanism of Salmonella-induced macrophage cytotoxicity.
- To determine the role of membrane ruffling and intracellular replication in Salmonella-induced apoptosis.
- To explore the influence of macrophage activation state on Salmonella invasion and apoptosis.
Main Methods:
- Assessing cytoskeletal changes and membrane ruffling upon Salmonella infection.
- Quantifying bacterial invasion levels in macrophages.
- Analyzing host cell apoptosis using nuclear morphology, DNA fragmentation, and cytoplasmic vacuolization.
- Evaluating Salmonella-induced apoptosis in both resting and activated macrophages.
Main Results:
- Invasive Salmonella typhimurium induces apoptosis in macrophages, characterized by DNA fragmentation and altered nuclear morphology.
- Membrane ruffling is essential for initiating Salmonella-induced apoptosis, even in strains with impaired intracellular replication.
- Mutant Salmonella incapable of inducing membrane ruffling do not trigger apoptosis.
- Activated macrophages show a greater response to Salmonella invasion, suggesting upregulated pathways for programmed cell death.
Conclusions:
- Salmonella-induced macrophage apoptosis is dependent on the induction of membrane ruffling.
- Apoptosis may facilitate bacterial survival and evasion of the host immune response.
- Macrophage activation state influences the host's susceptibility to Salmonella-induced cell death.