Journal of Biological Chemistry
Volume 273, Issue 8, 20 February 1998, Pages 4725-4733
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CELL BIOLOGY AND METABOLISM
Molecular Comparison of Soluble Intercellular Adhesion Molecule (sICAM)-1 and sICAM-3 Binding to Lymphocyte Function-associated Antigen-1*

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The interactions of intercellular adhesion molecules-1 and -3 (ICAM-1 and ICAM-3) with lymphocyte function-associated antigen-1 (LFA-1) have been characterized and compared on the molecular and cellular level. Enzyme-linked immunosorbent-based molecular assays have been utilized to calculate the binding affinities of soluble ICAM-1 (sICAM-1) and soluble ICAM-3 (sICAM-3) for LFA-1. Consistent with previously published data, we found that sICAM-1 binds to LFA-1 with an affinity of ∼60 nm. In contrast, sICAM-3 binds to LFA-1 with an affinity ∼9 times weaker (∼550 nm). Both sICAM-1 and sICAM-3 require divalent cations for binding. Specifically, both Mg2+ and Mn2+ support high affinity adhesion, although interestingly, high concentrations of Ca2+decrease the affinity of each molecule for LFA-1 substantially. Furthermore, a panel of anti-LFA-1 monoclonal antibodies were characterized for their ability to block sICAM-1 and sICAM-3/LFA-1 interactions in molecular and cellular assays to help distinguish binding sites on LFA-1 for both molecules. Finally, molecular and cellular competition experiments demonstrate that sICAM-1 and sICAM-3 compete with each other for binding to LFA-1. The above data demonstrate that sICAM-1 and sICAM-3 share a common binding site or an overlapping binding site on LFA-1 and that the apparent differences in binding sites can be attributed to different affinities of sICAM-1 and sICAM-3 for LFA-1.

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This paper is dedicated to Enza and Joey.