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Salmonella typhimurium induces apoptosis in human monocyte-derived macrophages
1Children's Hospital of Pittsburgh, Department of Surgery, PA 15213, USA. ZhouX@CHPLINK.CHP.EDU
Abstract:
Salmonella species represent a leading cause of gastroenteritis worldwide. More recently, they have been proposed as putative vaccine delivery vehicles in humans. Oral infection with Salmonella leads to invasion of the intestinal epithelial barrier and subsequent interaction with mucosal macrophages. In this study, we investigated the fate of Salmonella typhimurium-infected human macrophages differentiated from blood monocytes by GM-CSF. Wild type S. typhimurium strain SL1344 induced macrophage surface blebbing and caused the release of host cytoplasmic lactate dehydrogenase beginning 30 min post-infection. Three hours later more than 80% of the macrophages in the culture were killed. In contrast, during the same period, macrophages infected with the non-invasive S. typhimurium strain BJ66 remained viable. Chromatin fragmentation is a hallmark of cells undergoing apoptosis. Using TUNEL analysis, we observed chromatin fragmentation in macrophages infected with SL1344 but not in BJ66 infected cells. Consistent with this observation, we found that pretreatment of human macrophages with an inhibitor of caspase-3, a member of the pro-apoptotic enzyme family shown to be involved in S. typhimurium-induced killing of mouse macrophages, reduced SL1344-mediated cytotoxicity by 40%. Our study provides the first evidence that invasive S. typhimurium induces apoptosis in human macrophages that were differentiated from blood monocytes by GM-CSF, and that cell death is a caspase-dependent phenomenon.
Insights
Invasive Salmonella typhimurium triggers apoptosis in human macrophages, a programmed cell death pathway dependent on caspase-3. This finding is crucial for understanding Salmonella pathogenesis and its potential as a vaccine vector.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Salmonella species are a major cause of gastroenteritis globally.
- Salmonella is being explored as a potential vaccine delivery vehicle.
- Salmonella infection involves breaching the intestinal barrier and interacting with macrophages.
Purpose of the Study:
- To investigate the impact of Salmonella typhimurium infection on human macrophages.
- To determine if Salmonella induces programmed cell death (apoptosis) in these cells.
- To elucidate the role of caspase-3 in Salmonella-induced macrophage death.
Main Methods:
- Human macrophages were differentiated from blood monocytes using GM-CSF.
- Macrophages were infected with invasive (SL1344) and non-invasive (BJ66) S. typhimurium strains.
- Cell viability was assessed by lactate dehydrogenase release.
- Apoptosis was detected using TUNEL analysis.
- Caspase-3 inhibition was used to evaluate its role in cytotoxicity.
Main Results:
- Invasive S. typhimurium (SL1344) caused significant macrophage death (>80%) within 3 hours.
- Non-invasive S. typhimurium (BJ66) did not induce cell death.
- TUNEL analysis confirmed chromatin fragmentation (apoptosis) in SL1344-infected macrophages.
- Inhibiting caspase-3 reduced SL1344-mediated cytotoxicity by 40%.
Conclusions:
- Invasive Salmonella typhimurium induces caspase-dependent apoptosis in human macrophages.
- This programmed cell death is a key mechanism in Salmonella pathogenesis.
- Understanding this process is vital for developing Salmonella-based vaccines.