Related Experiment Video
Updated: Jun 6, 2025
Time-lapse 3D Imaging of Phagocytosis by Mouse Macrophages
Published on: October 19, 2018
Spatial Discrimination Limit Analysis of Macrophage Phagocytosis Between Target Antigens and Non-Target Objects Using
Maiha Ando1, Dan Horonushi1, Haruka Yuki1
1Department of Pure and Applied Physics, Graduate School of Advanced Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan.
Abstract:
During phagocytosis, the FcGR-IgG bond is thought to be necessary to promote cell-membrane extension as the zipper mechanism. However, does this zipper mechanism provide a spatial antigen discrimination capability that allows macrophages to selectively phagocytose only antigens, especially for clusters with a mixture of antigens and non-antigens? To elucidate the ability and limitation of the zipper mechanism, we fed a coupled 2 μm IgG-coated and 4.5 μm non-coated polystyrene bead mixtures to macrophages and observed their phagocytosis. Macrophage engulfed the mixed clusters, including the 4.5 μm non-coated polystyrene part, indicating that the non-coated particles can be engulfed even without the zipper mechanism as far as coupled to the opsonized particles. In contrast, when the non-opsonized particle part was held by the microcapillary manipulation assay, macrophages pinched off the non-coated polystyrene particle part and internalized the opsonized particle part only. The results suggest that (1) an IgG-coated surface is needed to anchor phagocytosis by cell-membrane protrusion; however, (2) once the antibody-dependent cell phagocytosis is started, phagocytosis can proceed with the uncoated objects as the followers of the internalizing opsonized particles even without the support of the zipper mechanism. They may also indicate the concern of misleading the immune system to target unexpected objects because of their aggregation with target pathogens and the possibility of new medical applications to capture the non-opsonized target objects by the aggregation with small antigens to activate an immune response.
Insights
Macrophages can engulf non-antigens attached to opsonized particles, suggesting the zipper mechanism is not essential for spatial discrimination in phagocytosis. This has implications for immune system targeting and medical applications.
Area of Science:
- Immunology
- Cell Biology
- Biophysics
Background:
- Phagocytosis is a crucial immune process mediated by Fc gamma receptors (FcGR) and immunoglobulin G (IgG).
- The zipper mechanism, involving FcGR-IgG bonds, is believed to drive cell-membrane extension during phagocytosis.
- The capacity of this mechanism for spatial antigen discrimination remains unclear, particularly in mixed antigen/non-antigen clusters.
Purpose of the Study:
- To investigate the role and limitations of the zipper mechanism in phagocytosis.
- To determine if the zipper mechanism enables macrophages to selectively phagocytose antigens.
- To explore the spatial discrimination capabilities of macrophages when encountering mixed particle clusters.
Main Methods:
- Macrophages were fed mixtures of 2 μm IgG-coated and 4.5 μm non-coated polystyrene beads.
- Phagocytosis of these mixed clusters was observed.
- Microcapillary manipulation was used to hold non-opsonized particle parts during engulfment.
Main Results:
- Macrophages engulfed mixed clusters, including non-coated particles attached to opsonized particles.
- Non-coated particles were internalized even without direct zipper mechanism support, provided they were coupled to opsonized particles.
- When the non-opsonized part was manipulated, macrophages detached it, internalizing only the opsonized part.
Conclusions:
- An IgG-coated surface is essential for initiating phagocytosis via cell-membrane protrusion (zipper mechanism).
- Once initiated, phagocytosis can proceed with uncoated particles as followers, even without direct zipper mechanism support.
- Findings suggest potential for immune system misdirection by aggregated non-antigens and new medical applications for capturing targets via antigen aggregation.
