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Interferon production by Shigella flexneri-infected fibroblasts depends upon intracellular bacterial metabolism
C B Hess1, D W Niesel, J Holmgren
1Department of Microbiology, University of Texas Medical Branch, Galveston 77550.
Abstract:
The role of bacterial invasion and subsequent intracellular metabolism or replication, or both, in the induction of interferon (IFN) production in primary cultures of murine embryo fibroblasts (MEFs) was examined. IFN production appeared to be dependent upon bacterial invasion. MEFs that were challenged with Shigella flexneri cultured at 30 degrees C to inhibit the temperature-dependent virulence gene expression that is essential for invasion failed to produce IFN. Furthermore, inhibition of S. flexneri invasion by pretreatment of MEFs with cytochalasin B resulted in a reduction in IFN production. Intracellular bacterial residence alone, however, was not sufficient for the induction of IFN production since an avirulent isogenic variant of S. flexneri which invades but fails to grow intracellularly did not induce IFN production. In fact, the blocking of bacterial RNA synthesis immediately after cellular uptake of S. flexneri by rifampin inhibited IFN production by MEFs. Transfer of the invasion-encoding plasmid to a noninvasive Escherichia coli strain conferred upon the bacteria the ability to invade MEFs and induce IFN production. These results suggest that the induction of IFN production in S. flexneri-infected fibroblasts requires bacterial invasion and intracellular bacterial metabolism or replication, or both.
Insights
Bacterial invasion and intracellular activity are crucial for inducing interferon (IFN) production in fibroblasts. Without invasion or intracellular growth, IFN production is significantly reduced, highlighting key factors in host-pathogen interactions.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Interferon (IFN) production is a critical host defense mechanism against viral and bacterial infections.
- The precise mechanisms by which bacteria trigger IFN production in host cells are not fully understood.
- Bacterial invasion and intracellular survival are potential triggers for innate immune responses.
Purpose of the Study:
- To investigate the role of bacterial invasion and intracellular events in inducing interferon production.
- To determine if bacterial residence within host cells is sufficient for interferon induction.
- To elucidate the specific bacterial factors required for triggering interferon synthesis.
Main Methods:
- Primary cultures of murine embryo fibroblasts (MEFs) were challenged with Shigella flexneri strains.
- Invasion was inhibited using cytochalasin B and by culturing bacteria at a reduced temperature.
- Interferon production was measured following bacterial challenge and manipulation of bacterial intracellular activity.
- Bacterial RNA synthesis was inhibited using rifampin post-invasion.
- Genetic manipulation involved transferring invasion plasmids between bacterial strains.
Main Results:
- Interferon production was dependent on bacterial invasion; inhibition of invasion reduced IFN levels.
- Intracellular bacterial residence alone did not induce IFN production.
- An avirulent S. flexneri variant that invaded but did not replicate intracellularly failed to induce IFN.
- Blocking bacterial RNA synthesis immediately after invasion inhibited IFN production.
- Transfer of invasion plasmids to noninvasive E. coli conferred IFN-inducing ability.
Conclusions:
- Bacterial invasion is a prerequisite for interferon induction in fibroblasts.
- Intracellular bacterial metabolism or replication, or both, are necessary for robust IFN production.
- Specific bacterial virulence factors associated with invasion and intracellular survival are key to triggering interferon responses.