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Shigella flexneri is trapped in polymorphonuclear leukocyte vacuoles and efficiently killed
I Mandic-Mulec1, J Weiss, A Zychlinsky
1The Skirball Institute, New York University School of Medicine, New York, New York 10016, USA.
Abstract:
We examined the bactericidal activity of polymorphonuclear leukocytes (PMN) against an invasive wild-type strain of Shigella flexneri (M90T) and a plasmid-cured noninvasive derivative (BS176). Both Shigella strains, as well as a rough strain of Escherichia coli, were killed with similar efficiencies by intact inflammatory PMN in room air and under N2 (i.e., killing was O2 independent). Bacterial killing by PMN extracts was substantially inhibited by antibodies to the bactericidal/permeability-increasing protein (BPI). Whereas wild-type Shigella escapes from the phagosome to the cytoplasm in epithelial cells and macrophages, wild-type Shigella was trapped in the phagolysosome of PMN as visualized by electron microscopy. The efficient killing of Shigella by PMN suggests that these inflammatory cells may not only contribute initially to the severe tissue damage characteristic of shigellosis but also ultimately participate in clearance and resolution of infection.
Insights
Polymorphonuclear leukocytes (PMN) efficiently kill Shigella bacteria, independent of oxygen. This suggests PMNs play a key role in clearing Shigella infections and resolving inflammation.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Shigellosis is a severe diarrheal disease caused by Shigella bacteria.
- The role of polymorphonuclear leukocytes (PMN) in Shigella infection clearance is not fully understood.
- Shigella exhibits different intracellular behaviors in various host cells.
Purpose of the Study:
- To investigate the bactericidal activity of PMN against Shigella flexneri.
- To determine the mechanisms involved in PMN-mediated killing of Shigella.
- To elucidate the intracellular fate of Shigella within PMN.
Main Methods:
- Bactericidal assays using intact PMN and PMN extracts against Shigella flexneri strains.
- Oxygen-independent killing assays.
- Inhibition assays using antibodies against bactericidal/permeability-increasing protein (BPI).
- Electron microscopy to visualize bacterial-host cell interactions.
Main Results:
- PMN efficiently killed both invasive and noninvasive Shigella strains, as well as Escherichia coli.
- Bacterial killing by PMN extracts was inhibited by anti-BPI antibodies, indicating BPI's role.
- Unlike in epithelial cells and macrophages, wild-type Shigella was trapped within the phagolysosome of PMN.
- Killing was effective in both aerobic and anaerobic conditions, suggesting oxygen independence.
Conclusions:
- PMN possess potent bactericidal activity against Shigella.
- Bactericidal/permeability-increasing protein (BPI) contributes to PMN-mediated killing.
- PMN effectively contain Shigella within phagolysosomes, preventing cytoplasmic escape.
- PMN are crucial for both the pathogenesis and resolution of shigellosis.