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Differential ligand binding specificities of recombinant CD11b/CD18 integrin I-domain
1R. W. Johnson Pharmaceutical Research Institute, Don Mills, Ontario, Canada.
The Journal of Biological Chemistry
|June 24, 1994
Summary
The CD11b I-domain binds fibrinogen and ICAM-1, crucial for leukocyte adhesion. This domain is key for receptor activation, but less involved in factor X recognition.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Leukocyte integrins, specifically CD11/CD18, play vital roles in cell adhesion and immune responses.
- The alpha subunits of these integrins possess an I-domain, a critical region for ligand interaction.
Purpose of the Study:
- To investigate the direct interaction of the recombinant CD11b I-domain with known integrin ligands.
- To determine the role of the CD11b I-domain in receptor activation and ligand binding specificity.
Main Methods:
- Generation and analysis of a recombinant CD11b I-domain.
- Binding assays using radiolabeled ligands (fibrinogen, factor X) and monoclonal antibodies.
- Inhibition studies with unlabeled ligands, peptides, and antibodies.
Main Results:
- The CD11b I-domain bound fibrinogen and intercellular adhesion molecule-1 in a concentration-dependent manner.
- Binding of 125I-fibrinogen was saturable with a Kd of ~0.22 microM and inhibited by unlabeled fibrinogen and a specific peptide.
- Factor X binding was only partially inhibited and unaffected by blocking antibodies, suggesting minimal I-domain involvement.
Conclusions:
- The CD11b I-domain is essential for binding fibrinogen and ICAM-1, mediating key adhesive interactions.
- This domain contributes to the qualitative aspects of CD11b/CD18 receptor activation.
- The I-domain shows limited involvement in the recognition of factor X by CD11b/CD18.