Related Experiment Videos
Endocytosis of the C3b receptor of complement within coated pits in human polymorphonuclear leukocytes and monocytes
Insights
Human immune cells use C3b receptors to internalize substances. These receptors cluster on the cell surface and then move inside cells via coated pits and vesicles, ultimately reaching lysosomes.
Area of Science:
- Immunology
- Cell Biology
- Microscopy
Background:
- The C3b receptor plays a crucial role in the innate immune system.
- Understanding receptor-mediated endocytosis is vital for immune cell function.
Purpose of the Study:
- To visualize the distribution and endocytosis of the C3b receptor in human immune cells.
- To elucidate the mechanism of C3b receptor internalization.
Main Methods:
- Fluorescent and electron microscopy were used to examine labeled human polymorphonuclear leukocytes and monocytes.
- Cells were labeled with anti-C3b receptor antibodies conjugated to rhodamine or ferritin.
Main Results:
- C3b receptors were observed in clusters on the plasma membrane at low temperatures.
- Upon warming, receptors were internalized via coated endocytic pits and vesicles.
- Receptor-antibody complexes were found in lysosomes after prolonged incubation.
Conclusions:
- C3b receptors directly mediate endocytosis through coated pits.
- This mechanism is shared with other receptors for efficient ligand internalization.
Abstract:
The distribution and endocytosis of the C3b receptor by human polymorphonuclear leukocytes and monocytes were visualized by both fluorescent and electron microscopic examination of cells that had been labeled with monospecific F(ab')2 anti-C3b receptor and anti-F(ab')2 conjugated with rhodamine or ferritin. When prefixed or unfixed cells that were labeled at 0 to 4 degrees C were examined, the receptor was distributed within clusters on the plasma membrane. After the cells had been warmed to room temperature or to 37 degrees C for 5 minutes, the fluorescently labeled receptors appeared to enter the cells, and the ferritin-tagged receptors often occurred within coated endocytic pits and coated vesicles within the cytoplasm. After incubation at 37 degrees C for 20 minutes, the C3b receptor-antibody complexes were largely cleared from the cell surface, and much of the label was found within lysosomes. These results indicate that C3b receptors may directly mediate endocytosis within coated pits, thus utilizing a mechanism shared by a variety of other receptors for the rapid, efficient, and selective internalization of extracellular ligands.