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Published on: July 17, 2013
Streptococcus pyogenes bacteria modulate membrane traffic in human neutrophils and selectively inhibit azurophilic
Leïla Staali1, Susanne Bauer, Matthias Mörgelin
1Department of Clinical Sciences, Section for Clinical and Experimental Infectious Medicine, BMC, B14, Lund University, Tornavägen 10, SE-221 84 Lund, Sweden.
Abstract:
We recently reported that the human pathogen Streptococcus pyogenes of the M1 serotype survives and replicates intracellularly after being phagocytosed by human neutrophils. These data raised the possibility that the generation of reactive oxygen metabolites by neutrophils, and the release of microbicidal molecules from their azurophilic and specific granules into phagosomes, can be modulated by S. pyogenes bacteria expressing surface-associated M and/or M-like proteins. We now demonstrate, using flow cytometry, immunofluorescence microscopy and transmission electron microscopy, that live wild-type S. pyogenes, after internalization by human neutrophils, inhibits the fusion of azurophilic granules with phagosomes. In contrast, azurophilic granule-content is efficiently delivered to phagosomes containing bacteria not expressing M and/or M-like proteins. Also, when heat-killed wild-type bacteria are used as the phagocytic prey, fusion of azurophilic granules with phagosomes is observed. The inhibition caused by live wild-type S. pyogenes is specific for azurophilic granule-phagosome fusion, because the mobilization of specific granules and the production of reactive oxygen species are induced to a similar extent by all strains tested. In conclusion, our results demonstrate that viable S. pyogenes bacteria expressing M and M-like proteins selectively prevent the fusion of azurophilic granules with phagosomes.
Insights
Streptococcus pyogenes (S. pyogenes) M1 serotype bacteria prevent neutrophils from delivering microbicidal molecules by inhibiting azurophilic granule fusion with phagosomes. This mechanism aids bacterial survival within immune cells.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Streptococcus pyogenes (S. pyogenes) M1 serotype survives and replicates within human neutrophils.
- Neutrophils utilize reactive oxygen metabolites and granule contents to kill phagocytosed bacteria.
- Surface proteins of S. pyogenes may modulate neutrophil microbicidal activity.
Purpose of the Study:
- To investigate whether S. pyogenes expressing M and M-like proteins can inhibit neutrophil microbicidal mechanisms.
- To determine the effect of S. pyogenes internalization on azurophilic and specific granule fusion with phagosomes.
Main Methods:
- Flow cytometry
- Immunofluorescence microscopy
- Transmission electron microscopy
- Phagocytosis assays using human neutrophils and various S. pyogenes strains (live wild-type, non-M protein expressing, heat-killed).
Main Results:
- Live wild-type S. pyogenes expressing M/M-like proteins significantly inhibited azurophilic granule fusion with phagosomes.
- Phagosomes containing S. pyogenes lacking M/M-like proteins or heat-killed bacteria showed efficient azurophilic granule fusion.
- Specific granule mobilization and reactive oxygen species production were unaffected by live wild-type S. pyogenes.
Conclusions:
- Viable S. pyogenes expressing M and M-like proteins selectively block azurophilic granule fusion with phagosomes.
- This selective inhibition represents a novel mechanism for S. pyogenes to evade neutrophil-mediated killing.
- The findings highlight a specific bacterial evasion strategy targeting a key innate immune process.
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