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Specialization of the macrophage plasma membrane at sites of interaction with opsonized erythrocytes
Abstract:
We incubated mouse peritoneal macrophages for 3-8 min at 37 degrees C with antibody-coated sheep erythrocytes and examined regions of close interaction between the two cell types by electron microscopy. At sites of focal macrophage-erythrocyte contact we observed a distinctive specialization of the macrophage plasma membrane consisting of a prominent subplasmalemmal band of electron-dense material, approximately 25-35 nm in thickness. In many instances, this band showed a periodic substructure similar to that seen in clathrin coats. Moreover, many slender erythrocyte processes penetrated into invaginations of the macrophage surface which were bristle-coated at their blind extremity. As previously shown for clathrin-coated pits, the segments of the macrophage plasma membrane beneath which the defense material was found were selectively resistant to the membrane-perturbing effect of the antibiotic, filipin. This structural specialization of the macrophage plasma membrane at sites of ligand-receptor interaction during immune phagocytosis of antibody-coated erythrocytes may represent the morphological counterpart of the zipper mechanism of phagocytosis previously demonstrated by functional studies.
Insights
Electron microscopy revealed a specialized membrane structure on macrophages during immune phagocytosis. This structure, resembling clathrin coats, may facilitate the zipper mechanism of phagocytosis.
Area of Science:
- Cell Biology
- Immunology
- Microscopy
Background:
- Phagocytosis is a crucial cellular process for immune defense.
- The precise molecular mechanisms underlying phagocytosis, particularly the initial cell-cell interactions, are not fully understood.
Purpose of the Study:
- To investigate the ultrastructural changes in macrophage plasma membranes during immune phagocytosis of antibody-coated erythrocytes.
- To identify specialized membrane domains involved in the early stages of phagocytosis.
Main Methods:
- Incubation of mouse peritoneal macrophages with antibody-coated sheep erythrocytes.
- Examination of macrophage-erythrocyte interaction sites using high-resolution electron microscopy.
- Assessment of membrane resistance to filipin to identify specialized lipid domains.
Main Results:
- Observed a distinct subplasmalemmal electron-dense band (25-35 nm) at focal macrophage-erythrocyte contact sites.
- This band exhibited a periodic substructure similar to clathrin coats.
- Macrophage membrane invaginations with erythrocyte processes were coated and resistant to filipin, suggesting specialized lipid organization.
Conclusions:
- Identified a novel structural specialization of the macrophage plasma membrane during immune phagocytosis.
- This specialization may represent the morphological basis of the 'zipper' mechanism of phagocytosis.
- The findings provide insights into the molecular and structural events governing immune cell interactions and engulfment.