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Distribution of annexin I during non-pathogen or pathogen phagocytosis by confocal imaging and immunogold electron
M C Harricane1, E Caron, F Porte
1INSERM U-249, CRBM du CNRS, Université Montpellier I, France.
Abstract:
Annexin I is an abundant protein in U937 cells differentiated towards a macrophagic phenotype. These cells become able to kill Escherichia coli, however, the intracellular pathogen Brucella suis, known to interfere with phagosome maturation, multiply in these differentiated cells. We have analysed by confocal and electron microscopy the cellular localization of annexin I during phagocytosis of yeast, non-pathogenic E. coli and the intracellular pathogen B. suis. Using immunocytochemical detections annexin I was found mainly as patches in the cytoplasm of uninfected cells. Upon phagocytosis of yeast or E. coli organisms, annexin I rapidly translocated and concentrated around phagosomes. On the other hand, annexin I was never detected around live B. suis-containing phagosomes. However, when dead brucellae were used, annexin I did translocate to the periphagosomal region. Our results suggest that annexin I could play a role in the molecular mechanism of phagosome maturation, which is impaired by some intracellular pathogens.
Insights
Annexin I protein aids phagosome maturation in U937 cells during E. coli infection. However, the pathogen Brucella suis prevents annexin I translocation, hindering phagosome maturation and allowing bacterial multiplication.
Area of Science:
- Cell Biology
- Immunology
- Microbiology
Background:
- Annexin I is abundant in U937 cells with macrophagic phenotype.
- These cells phagocytose Escherichia coli but are susceptible to Brucella suis.
- Brucella suis interferes with phagosome maturation.
Purpose of the Study:
- To investigate the cellular localization of annexin I during phagocytosis.
- To determine annexin I's role in phagosome maturation.
- To understand how Brucella suis affects annexin I localization.
Main Methods:
- Confocal microscopy
- Electron microscopy
- Immunocytochemical detection
- Phagocytosis assays with yeast, E. coli, and B. suis
Main Results:
- Annexin I translocated to phagosomes containing yeast and E. coli.
- Annexin I did not localize to phagosomes with live B. suis.
- Annexin I localized to phagosomes with dead B. suis.
Conclusions:
- Annexin I may be involved in phagosome maturation.
- Live B. suis may evade annexin I-mediated phagosome maturation.
- Annexin I's role in phagosome maturation is pathogen-dependent.