Red-cell ICAM-4 is a ligand for the monocyte/macrophage integrin CD11c/CD18: characterization of the binding sites on ICAM-4

摘要

Intercellular adhesion molecule-4 (ICAM-4) is a unique member of the ICAM family due to its specific expression on erythroid cells and ability to interact with several types of integrins expressed on blood and endothelial cells. The first reported receptors for ICAM-4 were CD11a/CD18 and CD11b/CD18. In contrast to these two, the cellular ligands and the functional role of the third beta2-integrin, CD11c/CD18, have not been well defined. Here we show that ICAM-4 functions as a ligand for the monocyte/macrophage specific CD11c/CD18. Deletion of the individual immunoglobulin domains of ICAM-4 demonstrated that both its domains contain binding sites for CD11c/CD18. Analysis of a panel of ICAM-4 point mutants identified residues that affected binding to the integrin. By molecular modeling the important residues were predicted to cluster in two distinct but spatially close regions of the first domain with an extension to the second domain spatially distant from the other residues. We also identified two peptides derived from sequences of ICAM-4 that are capable of modulating the binding to CD11c/CD18. CD11c/CD18 is expressed on macrophages in spleen and bone marrow. Inhibition of erythrophagocytosis by anti-ICAM-4 and anti-integrin antibodies suggests a role for these interactions in removal of senescent red cells.