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Flow analysis of MHC molecules and other membrane proteins in isolated phagosomes
L Ramachandra1, R M Sramkoski, D H Canaday
1Institute of Pathology, Case Western Reserve University, Cleveland, OH 44106, USA.
Abstract:
A method was developed to apply flow cytometry analysis to the characterization of individual phagosomes. Macrophages were incubated with latex beads and homogenized to release the phagosomes. Intact cells and nuclei were removed by low speed centrifugation, and a crude phagosome preparation was fixed with paraformaldehyde. Distinct optical properties of latex bead phagosomes allowed their analytic isolation from other organelles and cell fragments by flow analysis using a narrow gate based on scatter parameters. Furthermore, separate gates were established for phagosomes containing one, two and even three beads, which were sorted and examined by electron microscopy (EM). EM showed that the phagosomal membrane was closely apposed to the latex bead in most phagosomes, but some more spacious phagosomes were also observed. Phagosomes were immunolabeled and subjected to flow analysis for MHC-I and MHC-II molecules and lysosomal membrane markers (LAMPs). The proportion of LAMP-positive phagosomes increased with incubation time, reflecting maturation of phagolysosomes. Significant staining for MHC-I and MHC-II was demonstrated and remained relatively constant with time. Flow analysis of phagosomes allows the characterization and comparison of individual phagosomes, and the identification of subpopulations of phagosomes with differing membrane compositions. It also provides the advantage of analytically isolating phagosomes from other components of the cell without the need for extensive prior physical purification. Thus, it can be used to rapidly assess changes in phagosomal membrane composition as a function of phagosome maturation.
Insights
Flow cytometry enables detailed characterization of individual phagosomes, revealing insights into their membrane composition and maturation processes. This method isolates phagosomes efficiently for rapid analysis of cellular immune responses.
Area of Science:
- Immunology
- Cell Biology
- Biotechnology
Background:
- Phagosomes are crucial for cellular immunity and antigen presentation.
- Characterizing individual phagosomes and their membrane composition is challenging.
- Existing methods require extensive purification, limiting rapid analysis.
Purpose of the Study:
- To develop and validate a flow cytometry method for analyzing individual phagosomes.
- To characterize phagosome maturation and membrane composition.
- To enable rapid assessment of phagosomal changes.
Main Methods:
- Macrophages incubated with latex beads, homogenized, and centrifuged to isolate phagosomes.
- Flow cytometry used for analytic isolation based on scatter parameters.
- Phagosomes sorted, examined by electron microscopy, and immunolabeled for MHC and LAMPs.
Main Results:
- Flow cytometry successfully isolated latex bead phagosomes based on distinct optical properties.
- Electron microscopy confirmed phagosome integrity and membrane association with beads.
- Increased lysosomal membrane markers (LAMPs) observed with incubation time, indicating maturation.
- MHC-I and MHC-II molecules detected on phagosomes, remaining relatively constant over time.
Conclusions:
- Flow cytometry provides a powerful tool for characterizing individual phagosomes and identifying subpopulations.
- This method allows for efficient isolation and analysis of phagosomes without extensive purification.
- The approach facilitates rapid assessment of phagosome maturation and membrane composition changes.