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Updated: Feb 16, 2026
Study of Phagolysosome Biogenesis in Live Macrophages
Published on: March 10, 2014
Renitence vacuoles facilitate protection against phagolysosomal damage in activated macrophages
Amanda O Wong1,2, Matangi Marthi3, Zachary I Mendel3
1Immunology Graduate Program, University of Michigan Medical School, Ann Arbor, MI 48109.
Abstract:
As professional phagocytes, macrophages are susceptible to endolysosomal membrane damage inflicted by the pathogens and noxious particles they ingest. Whether macrophages have mechanisms for limiting such damage is not well understood. Previously, we reported a phenomenon, termed "inducible renitence," in which lipopolysaccharide (LPS) activation of macrophages protected their endolysosomes against damage initiated by the phagocytosis of silica beads. To gain mechanistic insight into the process, we analyzed the kinetics of renitence and morphological features of LPS-activated versus resting macrophages following silica bead-mediated injury. We discovered novel vacuolar structures that form in LPS-activated but not resting macrophages following silica bead phagocytosis. Because of their correlation with renitence and damage-resistant nature, we termed these structures "renitence vacuoles" (RVs). RVs formed coincident with silica bead uptake in a process associated with membrane ruffling and macropinocytosis. However, unlike normal macropinosomes (MPs), which shrink within 20 min of formation, RVs persisted around bead-containing phagosomes. RVs fused with lysosomes, whereas associated phagosomes typically did not. These findings are consistent with a model in which RVs, as persistent MPs, prevent fusion between damaged phagosomes and intact lysosomes and thereby preserve endolysosomal integrity.
Insights
Macrophages possess a defense mechanism called inducible renitence, involving novel "renitence vacuoles" (RVs), which protect against pathogen-induced endolysosomal damage. These RVs prevent phagosome-lysosome fusion, preserving cellular integrity.
Area of Science:
- Cell Biology
- Immunology
- Pathology
Background:
- Macrophages, as professional phagocytes, are vulnerable to endolysosomal damage from ingested pathogens and particles.
- The mechanisms by which macrophages limit such damage are not fully understood.
- Previous work identified "inducible renitence" as LPS-activated macrophage protection against silica bead-induced endolysosomal damage.
Purpose of the Study:
- To investigate the mechanistic basis of inducible renitence in macrophages.
- To analyze the kinetics and morphology of LPS-activated macrophages responding to silica bead injury.
- To identify cellular structures involved in protecting endolysosomes.
Main Methods:
- Comparative analysis of LPS-activated and resting macrophages after silica bead phagocytosis.
- Kinetic and morphological studies of cellular responses to injury.
- Microscopy and cell biology techniques to characterize novel vacuolar structures.
Main Results:
- Discovered novel "renitence vacuoles" (RVs) in LPS-activated macrophages, absent in resting cells, following silica bead uptake.
- RVs formed concurrently with phagocytosis, involving membrane ruffling and macropinocytosis.
- Unlike normal macropinosomes, RVs persisted around bead-containing phagosomes and fused with lysosomes, while phagosomes did not.
Conclusions:
- RVs are persistent macropinosomes that play a crucial role in inducible renitence.
- RVs act as a protective mechanism by preventing fusion between damaged phagosomes and intact lysosomes.
- This process preserves overall endolysosomal integrity in activated macrophages.
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