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The leukocyte cell surface receptor(s) for the iC3b product of complement
Insights
Complement receptor 3 (CR3) is a key adhesion molecule on immune cells, involved in phagocytosis and cell migration. Its interactions with various ligands, including bacterial lipopolysaccharide (LPS), are crucial for immune responses.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Complement receptor 3 (CR3) is a major adhesion molecule on monocytes and neutrophils.
- CR3's role as a phagocytic receptor for iC3b-coated particles is well-established.
- CR3 binds to diverse ligands, including fibrinogen, factor X, beta-glucan, and bacterial LPS.
Purpose of the Study:
- To investigate the function and ligand-binding properties of CR3.
- To identify the ligand recognized by CR3 on endothelial cells, crucial for monocyte and neutrophil migration.
- To explore the structural relationships and shared affinities of leukocyte integrins (CR3, p150,95, LFA-1).
Main Methods:
- Characterization of CR3's phagocytic receptor function.
- Analysis of CR3's binding affinities for various ligands.
- Investigation of CR3's role in leukocyte extravascular migration.
- Structural comparison with related integrins (p150,95, LFA-1).
Main Results:
- CR3 exhibits broad ligand-binding capabilities beyond iC3b, including bacterial LPS.
- CR3's interaction with endothelial cells is implicated in leukocyte migration, though the specific ligand remains unidentified.
- CR3, p150,95, and LFA-1 are leukocyte-specific integrins sharing affinity for bacterial LPS.
Conclusions:
- CR3 is a multifunctional adhesion molecule with significant roles in innate immunity and cell trafficking.
- Further research is needed to elucidate the endothelial ligand for CR3 and the functional significance of p150,95 as a complement receptor.
Abstract:
CR3 is probably the major adhesion molecule on monocytes and neutrophils. Its function as a phagocytic receptor for iC3b-coated particles has been well characterized. CR3 also has binding affinity for other ligands, including those that compete with iC3b such as fibrinogen, factor X, and beta-glucan, and those that do not such as bacterial LPS. CR3 binding to endothelial cells probably plays an important role in the extravascular migration of monocytes and neutrophils, but the ligand that it recognizes on endothelial cells has not been identified. Structurally CR3 belongs to the integrin family, and it shares a common subunit with p150,95 and LFA-1. The expression of these three membrane antigens appear to be limited to leukocytes, and they are sometimes referred to collectively as the leukocyte integrins. All three antigens have a common binding affinity for bacterial LPS. p150,95 also has affinity for iC3b, but p150,95/iC3b-dependent cellular responses has not been demonstrated. Its status as a complement receptor therefore awaits further experimental support.