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Rate and extent of phagocytosis in macrophages lacking vamp3
Lee-Ann H Allen1, Chunmei Yang, Jeffrey E Pessin
1Department of Internal Medicine, University of Iowa, 200 Hawkins Drive, Iowa City, IA 52242, USA. lee-ann-allen@uiowa.edu
Abstract:
During phagocytosis, macrophages rapidly internalize a substantial fraction of plasma membrane without a net loss of surface area, suggesting that membranes are targeted to the cell surface from intracellular sites. Nevertheless, a requirement for mobilization of specific membrane compartments has not been demonstrated. We used bone marrow-derived macrophages (BMM) from wild type and vamp3 null mice to evaluate directly the requirement for this v-SNARE in phagocytosis of zymosan, IgG-beads, complement-opsonized particles, or latex microspheres. Regardless of the phagocytic receptor engaged or particle load, BMM lacking vamp3 exhibited no phagocytic defects when assayed after 1 h at 37 degrees C, and phagosome maturation was unimpaired as judged by acquisition of lamp-1. In contrast, at early time points (5-15 min), internalization of zymosan (but not other particles tested) was significantly slower in vamp3 null BMM. These data indicate that vamp3 modulates efficient uptake of zymosan, but is not absolutely required for phagocytosis in primary macrophages.
Insights
Vesicle-associated membrane protein 3 (vamp3) is not essential for macrophage phagocytosis. However, vamp3 does play a role in the efficient uptake of zymosan particles by macrophages.
Area of Science:
- Cell Biology
- Immunology
- Molecular Biology
Background:
- Macrophages internalize significant plasma membrane during phagocytosis without net surface area loss.
- This suggests intracellular membrane mobilization is crucial, but specific compartments involved remain unclear.
Purpose of the Study:
- To investigate the role of vesicle-associated membrane protein 3 (vamp3) in macrophage phagocytosis.
- To determine if vamp3 is required for membrane trafficking during phagocytosis.
Main Methods:
- Utilized bone marrow-derived macrophages (BMM) from wild type and vamp3 null mice.
- Assayed phagocytosis of various particles (zymosan, IgG-beads, complement-opsonized particles, latex microspheres).
- Evaluated phagosome maturation by assessing Lamp-1 acquisition.
Main Results:
- Vamp3-deficient BMM showed no overall phagocytic defects after 1 hour at 37°C.
- Phagosome maturation was unimpaired in vamp3 null BMM.
- Early zymosan internalization (5-15 min) was significantly slower in vamp3 null BMM, but other particle uptake was unaffected.
Conclusions:
- Vamp3 is not essential for general phagocytosis or phagosome maturation in primary macrophages.
- Vamp3 modulates, but is not absolutely required for, efficient zymosan uptake.
- Specific roles for vamp3 in particle-dependent phagocytic processes are suggested.