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Binding of mannosylated ferritin to chicken bone marrow macrophages
Abstract:
Ferritin conjugated to diazo p-aminophenylmannoside and mannan was used for ultrastructural visualization of binding and endocytosis via the mannose receptor. Conjugates were bound by live macrophages but not by glutaraldehyde-fixed cells. Binding was inhibited by 0.1 mM mannan and 0.2 M alpha-methylmannoside, and strongly reduced, but not abolished, after trypsin degradation of surface receptors. Binding sites were rapidly assembled on coated pits, which often showed a polar distribution on the cell surface and entered the cell following the direction of microtubuli. Some coated vesicles occasionally kept in touch with the extracellular space. 10-min exposure to the conjugate resulted in changes in the surface morphology, such as a loss of infoldings and increased membrane tension. Ferritin accumulated in large smooth vesicles with coated membrane regions. It was mostly detached from the membrane and agglutinated into big clumps, together with fibrillar material and small vesicles which may derive from the vesicle membrane.
Insights
Researchers visualized macrophage mannose receptor binding and endocytosis using ferritin conjugates. Live cells bound the conjugate, which was inhibited by mannan and alpha-methylmannoside, indicating receptor-mediated uptake.
Area of Science:
- Cell Biology
- Immunology
- Microscopy
Background:
- The mannose receptor plays a crucial role in cellular uptake and immune responses.
- Understanding the dynamics of receptor-mediated endocytosis is vital for various biological processes.
Purpose of the Study:
- To ultrastructurally visualize the binding and endocytosis of ligands by the mannose receptor.
- To investigate the cellular mechanisms involved in mannose receptor-mediated endocytosis.
Main Methods:
- Utilized ferritin conjugated to diazo p-aminophenylmannoside and mannan for ultrastructural visualization.
- Employed live and glutaraldehyde-fixed macrophages to study conjugate binding.
- Investigated the effects of mannan, alpha-methylmannoside, and trypsin on conjugate binding.
Main Results:
- Ferritin conjugates were bound by live macrophages, but not fixed cells, demonstrating specific receptor interaction.
- Binding was inhibited by mannan and alpha-methylmannoside, confirming mannose receptor involvement.
- Binding sites assembled on coated pits, which trafficked intracellularly along microtubules, and induced surface morphology changes.
Conclusions:
- The study provides ultrastructural evidence of mannose receptor-mediated endocytosis in macrophages.
- Ferritin-mannose conjugates effectively visualize the dynamic process of receptor binding and intracellular trafficking.
- Macrophage surface morphology is altered upon conjugate exposure, suggesting active endocytic processes.