ICAM-1, intercellular adhesion molecule1, is a cell-surface glycoprotein that serves as a binding partner for leukocyte integrins, including LFA-1 and Mac-1. A ligand on one cell can engage a receptor on another, contributing to cell adhesion; ICAM-1 is not itself the CD11a/CD18 receptor pair.
A 1987 reconstitution experiment made the interaction testable. Purified ICAM-1 was placed in artificial supported lipid bilayers. Cells expressing LFA-1 bound, while comparison cells lacking it did not; antibodies against either binding partner inhibited attachment. Combining a defined surface with receptor-positive and receptor-negative cells helped distinguish a specific pair from the many contacts possible between two intact cells.[ref]
An illustrative assay should count attachment under the same washing conditions and compare both missing-ligand and blocking controls. Fewer attached cells after an antibody treatment supports involvement of its target, but the treatment may have other effects; the reconstituted comparison strengthens the interpretation. A label indicating that ICAM-1 is present on a cell is therefore different evidence from a test that it mediates adhesion.
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