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Updated: May 1, 2026
Time-lapse 3D Imaging of Phagocytosis by Mouse Macrophages
Published on: October 19, 2018
Submicrometre sampling of living cells by macrophages
Amy C Fan1, Rukman R Thota2,3, Nina Serwas2,4
1Department of Pathology, University of California, San Francisco, San Francisco, CA, USA. amy.fan@ucsf.edu.
An effective immune system must sample and develop healthy self-identity to prevent autoimmunity and to discern pathogenic insults1-3. Self-proteins are presented to T cells in the thymus during immune cell development2,3 and must be presented throughout the body to maintain regulatory T cell populations4-6 and to provide tonic signals to sustain conventional T cells over time7-9. Observations of continuous apoptosis in some organs together with the ingestion of that material by myeloid populations has led to a conventional understanding of ongoing cell death as a major source of self-antigens10. Here we used a series of companion imaging and vesicular labelling technologies to reveal an alternative process undertaken by macrophages that results in non-destructive, direct sampling of living cells. This process requires cell-cell contact, does not require caspase activation and occurs via trogocytosis-like stretching of the target cell into the macrophage, which leads to the generation of submicrometre-sized vesicles that contain cytoplasm. Using a high-dimensional flow-based method for labelling vesicles, we demonstrate that live-sampled material is distinctly processed and is poorly subjected to fusion with lysosomes. The material also produces differential effects on the presentation of antigen to CD4 T cells compared with CD8 T cells. Disruption of this trafficking by redirecting antigen to the lysosome significantly reduced the associated macrophage-mediated priming of CD8 T cells. These results demonstrate an important and substantial sampling of living cells by the immune system, with clear consequences for maintaining the border of immunity.
An effective immune system must sample and develop healthy self-identity to prevent autoimmunity and to discern pathogenic insults1-3. Self-proteins are presented to T cells in the thymus during immune cell development2,3 and must be presented throughout the body to maintain regulatory T cell populations4-6 and to provide tonic signals to sustain conventional T cells over time7-9. Observations of continuous apoptosis in some organs together with the ingestion of that material by myeloid populations has led to a conventional understanding of ongoing cell death as a major source of self-antigens10. Here we used a series of companion imaging and vesicular labelling technologies to reveal an alternative process undertaken by macrophages that results in non-destructive, direct sampling of living cells. This process requires cell-cell contact, does not require caspase activation and occurs via trogocytosis-like stretching of the target cell into the macrophage, which leads to the generation of submicrometre-sized vesicles that contain cytoplasm. Using a high-dimensional flow-based method for labelling vesicles, we demonstrate that live-sampled material is distinctly processed and is poorly subjected to fusion with lysosomes. The material also produces differential effects on the presentation of antigen to CD4 T cells compared with CD8 T cells. Disruption of this trafficking by redirecting antigen to the lysosome significantly reduced the associated macrophage-mediated priming of CD8 T cells. These results demonstrate an important and substantial sampling of living cells by the immune system, with clear consequences for maintaining the border of immunity.
