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Macrophage-melanoma cell heterokaryons. IV. Unmasking the macrophage-specific membrane receptor
Abstract:
Mouse peritoneal macrophages possess a specific plasma membrane receptor for antibody-coated particles. Sheep red cells coated with rabbit 7S antibody attach readily to the macrophage surface and are subsequently interiorized. The fusion of macrophage with nonphagocytic mouse melanoma cells produces heterokaryons in which the macrophage receptor is drastically altered. The receptor is present shortly after fusion and heterokaryons are actively phagocytic. The ability to bind and ingest red cells is, however, progressively lost over the next 12-24 hr and does not reappear thereafter. Exposure of heterokaryons to trypsin (1-100 microg/ml for 30 min at 37 degrees C) results in the reappearance of initial receptor activity and the unmasking of the surface receptor. This property is again lost upon subsequent cultivation. The masking process takes place when cells are cultivated in the absence of IgG so that the adsorption of antibody from the medium is not responsible for this phenomenon. Inhibition of heterokaryon protein synthesis preserves phagocytic activity in a reversible fashion and prevents the masking of macrophage receptors. Inhibition of melanoma RNA synthesis before fusion is also able to block subsequent masking, but is ineffective if delayed until after fusion. Ultraviolet irradiation of the melanoma cell before fusion prevents subsequent masking, whereas similar treatment of the macrophage has no effect. Cells differ markedly in their ability to mask the macrophage phagocytic receptor after fusion. Ehrlich ascites tumor cells mask the receptor rapidly, primary chick fibroblasts minimally, and embryonic chick erythrocytes not at all.
Insights
Macrophages have a receptor for antibody-coated particles. Fusing macrophages with melanoma cells alters this receptor, causing phagocytosis to be lost over time, but trypsin can temporarily restore it.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Mouse peritoneal macrophages have a specific plasma membrane receptor for antibody-coated particles, mediating phagocytosis.
- Antibody-coated sheep red blood cells readily bind to and are internalized by macrophages.
Purpose of the Study:
- To investigate the alterations in macrophage phagocytic receptor activity after fusion with nonphagocytic mouse melanoma cells.
- To understand the mechanisms underlying the masking and unmasking of the macrophage receptor in heterokaryons.
Main Methods:
- Fusion of mouse peritoneal macrophages with mouse melanoma cells to create heterokaryons.
- Assessment of phagocytic activity and receptor binding in heterokaryons over time.
- Treatment of heterokaryons with trypsin, protein synthesis inhibitors, RNA synthesis inhibitors, and UV irradiation.
Main Results:
- Heterokaryons initially exhibit phagocytic activity, but receptor-mediated binding and ingestion are progressively lost within 12-24 hours.
- Trypsin treatment transiently restores receptor activity and unmasks the surface receptor.
- Inhibition of protein synthesis preserves phagocytic activity, while inhibition of melanoma RNA synthesis before fusion blocks masking.
- UV irradiation of melanoma cells before fusion prevents masking, but not if applied to macrophages.
Conclusions:
- Melanoma cell fusion leads to a reversible masking of the macrophage phagocytic receptor, dependent on melanoma cell factors.
- The masking process involves melanoma cell-derived components and is linked to protein synthesis and potentially RNA synthesis.
- Different cell types exhibit varying capacities to mask the macrophage phagocytic receptor following fusion.