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A contractile activity that closes phagosomes in macrophages
J A Swanson1, M T Johnson, K Beningo
1Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA. jswan@umich.edu
Journal of Cell Science
|January 14, 1999
Summary
Mouse macrophages use actin and myosin IC for contractile activity during phagocytosis. This purse-string-like mechanism closes phagosomes, enabling macropinosome and spacious phagosome formation.
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Fc-mediated phagocytosis is crucial for immune responses.
- Macrophage phagosome formation involves complex cellular dynamics.
- Actin dynamics and myosin motor proteins play key roles in cellular processes.
Purpose of the Study:
- To investigate the contractile mechanisms underlying phagosome formation in mouse macrophages.
- To identify the specific myosin isoforms involved in phagosome closure.
- To elucidate the role of contractile activity in the formation of macropinosomes and spacious phagosomes.
Main Methods:
- Time-lapse video microscopy of macrophages with fluorescently labeled actin and dextran.
- Inhibition studies using butanedione monoxime, wortmannin, and LY294002.
- Immunofluorescence microscopy to detect myosin localization within phagosomes.
Main Results:
- Actin concentrates at the distal margins of closing phagosomes.
- Contractile activity, observed during shared erythrocyte engulfment, was inhibited by myosins and phosphoinositide 3-kinase inhibitors.
- Myosin IC was specifically concentrated around the connecting membrane strings of shared phagosomes.
Conclusions:
- Myosin IC mediates the purse-string-like contraction essential for phagosome closure.
- This contractile mechanism explains the formation of macropinosomes and spacious phagosomes independently of particle surface guidance.