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Membrane sorting during phagocytosis: selective exclusion of major histocompatibility complex molecules but not
1Department of Medicine, School of Medicine, University of California, Los Angeles 90024.
Insights
Cells selectively exclude plasma membrane proteins during phagocytosis, creating a unique phagosome membrane. This process differs for conventional and coiling phagocytosis of bacteria like E. coli and L. pneumophila.
Area of Science:
- Cell Biology
- Immunology
- Microbiology
Background:
- Phagocytosis is a critical cellular process for engulfing pathogens and debris.
- The composition of the phagosome membrane is crucial for its function and interaction with the pathogen.
- Little is known about the dynamic changes in membrane protein distribution during different types of phagocytosis.
Purpose of the Study:
- To investigate the distribution of specific plasma membrane proteins during coiling phagocytosis of Legionella pneumophila and conventional phagocytosis of Escherichia coli.
- To determine if the cell selectively excludes certain membrane proteins from nascent phagosomes.
Main Methods:
- Immunocytochemical techniques were employed to visualize protein localization.
- Enzyme cytochemistry was used to assess the activity of specific enzymes associated with membrane proteins.
- The distribution of major histocompatibility complex (MHC) molecules, CR3 complement receptor, alkaline phosphatase, and 5'-nucleotidase was examined.
Main Results:
- Major histocompatibility complex (MHC) molecules were excluded from nascent phagosomes during both phagocytosis types.
- The CR3 complement receptor was found to persist in nascent phagosomes.
- Alkaline phosphatase activity was excluded from L. pneumophila coils and nascent phagosomes, similar to MHC molecules.
- 5'-nucleotidase activity showed intense staining in L. pneumophila coils, similar to CR3.
Conclusions:
- The cell selectively excludes certain plasma membrane proteins from nascent phagosomes during phagocytosis.
- Phagosomal membranes are distinct from the plasma membrane, with protein composition varying based on the phagocytosis mechanism and pathogen.
- This selective exclusion highlights the cell's sophisticated control over phagosome maturation and function.
Abstract:
We have used immunocytochemical techniques and enzyme cytochemistry to examine the distribution of plasma membrane proteins during coiling phagocytosis of Legionella pneumophila and conventional phagocytosis of Escherichia coli. Whereas class I and class II major histocompatibility complex (MHC) molecules are relatively excluded from nascent phagosomes during conventional and coiling phagocytosis, the CR3 complement receptor persists in nascent phagosomes. The staining pattern for alkaline phosphatase activity resembles that of MHC molecules, with a marked exclusion of phosphatase activity from L. pneumophila coils and nascent phagosomes. The staining pattern for 5'-nucleotidase activity, on the other hand, resembles that of CR3 with intense staining in the inner layers of L. pneumophila coils. These results demonstrate that the cell has the ability to exclude selectively certain membrane proteins from the nascent phagosome during phagocytosis, thereby producing a phagosomal membrane markedly different from the plasma membrane from which it is derived.