Detecting rapid and transient upregulation of leukocyte integrin affinity induced by chemokines and chemoattractants

The majority of integrins expressed on circulating leukocytes are quiescent and do not mediate adhesion. In the process of emigrating from blood into tissues, leukocytes are exposed to a variety of stimuli, including chemokines, which rapidly activate integrin function through changes in affinity and/or avidity. High affinity is brought about by a change in integrin conformation and results in formation of a stable bond with ligand. This can be measured in soluble ligand-binding assays. Integrin conformation changes also result in exposure of previously masked epitopes that can be detected with monoclonal antibodies. In this report, methods used to detect high affinity integrins are reviewed. Four different approaches are discussed, including detection of masked epitopes with monoclonal antibodies, and binding of soluble ligands, ligand-coated beads, and ligand-mimetic peptides. Improved techniques to measure rapid changes in integrin affinity in real time may be valuable both to study mechanisms of inside-out integrin activation and as a tool to screen for effective inhibitors of integrin activation in inflammatory disease models.