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A specific gene expression program triggered by Gram-positive bacteria in the cytosol.
Ramona L McCaffrey1, Paul Fawcett, Mary O'Riordan
1Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3202, USA.
Summary
This study reveals a distinct immune response pathway activated by pathogens entering the cell cytosol. It identifies interferon-responsive genes (IRGs) induced by cytosolic bacteria, independent of Toll-like receptor (TLR) signaling, enhancing understanding of pathogen detection.
Area of Science:
- Immunology
- Cellular Microbiology
- Molecular Biology
Background:
- Innate and adaptive immunity rely on recognizing pathogen-associated molecules, primarily via Toll-like receptors (TLRs) on cell surfaces.
- Mechanisms for detecting pathogens within cellular compartments, particularly the cytosol, and the resulting immune responses are poorly understood.
- Cytosolic pathogens like Listeria monocytogenes (Lm) present unique challenges for host immune surveillance.
Purpose of the Study:
- To investigate the gene expression program triggered by macrophages infected with cytosolic pathogens.
- To differentiate between TLR-dependent and independent immune responses to intracellular bacterial invasion.
- To identify specific pathways involved in cytosolic pathogen recognition.
Main Methods:
- Utilized mouse cDNA microarrays to analyze gene expression in bone marrow-derived macrophages infected with Listeria monocytogenes (Lm).
- Compared gene expression profiles following infection with wild-type Lm, heat-killed Lm, and Lm mutants lacking listeriolysin O.
- Investigated the role of cytosolic Bacillus subtilis (Bs) and Staphylococcus aureus (Sa) lipoteichoic acid in modulating immune responses.
Main Results:
- Identified two distinct gene expression clusters: early/persistent (NF-kappaB-dependent, TLR-associated) and late response (IFN-responsive genes, IRGs).
- The IRG cluster was dependent on Lm entry into the cytosol, requiring listeriolysin O for vacuole escape.
- Cytosolic Bacillus subtilis infection recapitulated the Lm-induced IRG expression profile, indicating a conserved cytosolic response pathway independent of MyD88-dependent TLR signaling.
Conclusions:
- A distinct, cytosol-specific transcriptional program exists, characterized by the induction of interferon-responsive genes (IRGs).
- This program is activated by pathogens escaping into the host cell cytosol and is independent of MyD88-mediated Toll-like receptor signaling.
- Further research into these cytosolic surveillance pathways and their interaction with TLR and IFN signaling is crucial for understanding host defense against intracellular pathogens.