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Published on: July 17, 2013
Membrane retrieval in neutrophils during phagocytosis: inhibition by M protein-expressing S. pyogenes bacteria
1Section for Molecular Pathogenesis, Department of Cell and Molecular Biology, BMC, B14, Lund University, Tornavägen 10, SE-221 84 Lund, Sweden.
Abstract:
During phagocytosis and phagosome maturation, complex membrane traffic events must be coordinated. We have observed, using fluorescent fluid-phase and membrane markers, that in the human neutrophil, internalization of nonopsonized, Gram-positive bacteria, but not of latex beads, is accompanied by a rapid and localized formation of pinosomal structures. This pinocytic response is calcium-dependent but insensitive to actin cytoskeleton disruption and wortmannin treatment. Contrary to what we observe, endosomal structures usually are considered to participate in phagosome formation by providing necessary membrane to forming phagosomes. Instead, our results show a coupling between neutrophil secretory and membrane-retrieval processes during phagosome maturation, and we suggest that the observed, localized pinocytic response is linked to the secretion of azurophilic granules toward nascent phagosomes. Accordingly, M and M-like protein-expressing Streptococcus pyogenes bacteria, which are able to survive inside neutrophil phagosomes, inhibit both the secretion of azurophilic granules to phagosomes and pinosome formation.
Insights
Neutrophils form pinosomes during bacterial phagocytosis, a calcium-dependent process linked to granule secretion. Streptococcus pyogenes inhibits this response, aiding its survival.
Area of Science:
- Cell Biology
- Immunology
- Microbiology
Background:
- Phagocytosis and phagosome maturation involve complex membrane trafficking in human neutrophils.
- Endosomal structures are typically thought to contribute membrane to forming phagosomes.
Purpose of the Study:
- To investigate membrane traffic events during the internalization of nonopsonized Gram-positive bacteria by human neutrophils.
- To elucidate the relationship between pinosome formation, granule secretion, and bacterial survival within phagosomes.
Main Methods:
- Utilized fluorescent fluid-phase and membrane markers to observe cellular processes.
- Investigated the role of calcium, actin cytoskeleton, and wortmannin in pinosome formation.
- Examined the impact of Streptococcus pyogenes on neutrophil secretory and membrane-retrieval processes.
Main Results:
- Internalization of Gram-positive bacteria, but not latex beads, induced rapid, localized pinosome formation in neutrophils.
- Pinosome formation was calcium-dependent but unaffected by actin disruption or wortmannin.
- A coupling between neutrophil secretory and membrane-retrieval processes during phagosome maturation was observed.
- Streptococcus pyogenes inhibited azurophilic granule secretion and pinosome formation, correlating with bacterial survival.
Conclusions:
- Neutrophil pinosome formation during bacterial phagocytosis is linked to azurophilic granule secretion.
- This localized pinocytic response appears to be a membrane-retrieval mechanism during phagosome maturation.
- Streptococcus pyogenes actively interferes with these neutrophil processes to promote intracellular survival.
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