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Cytotoxicity and interleukin-1beta processing following Shigella flexneri infection of human monocyte-derived
Jonathan D Edgeworth1, Jo Spencer, Armelle Phalipon
1Department of Infectious Diseases, St. George's Hospital Medical School, London, GB. j.edgeworth@sghms.ac.uk
Abstract:
Shigella flexneri infection of macrophages (MPhi) leads to activation of caspase-1 by the IpaB virulence factor, which induces rapid cell death and release of mature IL-1beta. Here we show that S. flexneri infection of human monocyte-derived dendritic cells (DC) also results in rapid IpaB-dependent death. Cytotoxicity is only partially blocked by the caspase-1 inhibitor YVAD, but completely blocked by the pan-caspase inhibitor z-VAD. Cytotoxicity is also partially blocked by glycine without affecting caspase-1-dependent IL-1beta processing, and treatment with glycine and YVAD completely blocks cytotoxicity, implying that glycine inhibits a caspase-1-independent cytotoxic mechanism. S. flexneri infection of LPS-pre-treated DC and Mphi results in comparable release of mature IL-1beta, although DC release significantly less IL-18 than MPhi. IL-1beta release from infected DC occurs within 3 h of the initial LPS pre-stimulation signal, implying that infection of DC will contribute towards induction of the early inflammatory response. The rapid death of DC during the early stages of shigellosis is likely to have adverse consequences for generation of adaptive immunity.
Insights
Shigella flexneri infection causes rapid cell death in dendritic cells (DC) via a caspase-1-independent mechanism. This early DC death during shigellosis may impair adaptive immunity development.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Shigella flexneri infection of macrophages (MPhi) activates caspase-1 via the IpaB virulence factor, inducing cell death and IL-1beta release.
- Dendritic cells (DC) are crucial for initiating immune responses, and their interaction with pathogens is critical for host defense.
Purpose of the Study:
- To investigate the mechanisms of Shigella flexneri-induced cell death in human monocyte-derived dendritic cells (DC).
- To compare the inflammatory responses, including IL-1beta and IL-18 release, between infected DC and MPhi.
- To assess the implications of rapid DC death on the generation of adaptive immunity during shigellosis.
Main Methods:
- Infection of human monocyte-derived DC and MPhi with S. flexneri.
- Treatment with caspase inhibitors (YVAD, z-VAD) and glycine to elucidate cell death pathways.
- Measurement of IL-1beta and IL-18 release using ELISA or similar assays.
- Assessment of cytotoxicity using cell viability assays.
Main Results:
- S. flexneri infection induced rapid IpaB-dependent cell death in DC, which was only partially blocked by caspase-1 inhibition but completely blocked by a pan-caspase inhibitor.
- Glycine partially blocked DC cytotoxicity independently of caspase-1 and IL-1beta processing, indicating a distinct cytotoxic pathway.
- Infected DC released mature IL-1beta rapidly (within 3 hours) after LPS pre-stimulation, comparable to MPhi, but released less IL-18 than MPhi.
- The rapid death of DC during early shigellosis suggests a potential negative impact on adaptive immune responses.
Conclusions:
- Shigella flexneri employs a potent IpaB-dependent cytotoxic mechanism against human dendritic cells, involving both caspase-dependent and -independent pathways.
- Early IL-1beta release by infected DC contributes to the inflammatory response, but rapid DC death may compromise the initiation of adaptive immunity in shigellosis.