title: Red-cell ICAM-4 is a ligand for the monocyte/macrophage integrin CD11c/CD18: characterization of the binding sites on ICAM-4.
abstract: Intercellular adhesion molecule 4 (ICAM-4) is a unique member of the ICAM family because of 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 2, 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 2 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 2 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.
authors.affiliation: Faculty of Biosciences, Division of Biochemistry, PO Box 56, Viikinkaari 5, University of Helsinki 00014, Finland.
authors.forename: Eveliina
authors.initials: E
authors.lastname: Ihanus
authors.forename: Liisa M
authors.initials: LM
authors.lastname: Uotila
authors.forename: Anne
authors.initials: A
authors.lastname: Toivanen
authors.forename: Minna
authors.initials: M
authors.lastname: Varis
authors.forename: Carl G
authors.initials: CG
authors.lastname: Gahmberg
mesh_terms: D001665:Binding Sites; D039521:CD11c Antigen / Q000187:drug effects / Q000378:metabolism*; D018821:CD18 Antigens / Q000187:drug effects / Q000378:metabolism*; D002448:Cell Adhesion / Q000187:drug effects / Q000235:genetics; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000494:pharmacology / Q000502:physiology*; D002460:Cell Line; D004912:Erythrocytes / Q000737:chemistry* / Q000276:immunology; D018014:Gene Transfer Techniques; D006801:Humans; D008024:Ligands; D008264:Macrophages / Q000187:drug effects* / Q000276:immunology; D008958:Models, Molecular; D009000:Monocytes / Q000187:drug effects* / Q000276:immunology; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology; D011487:Protein Conformation; D012995:Solubility; D013329:Structure-Activity Relationship
chemical_list: D039521:CD11c Antigen; D018821:CD18 Antigens; D015815:Cell Adhesion Molecules; C095100:ICAM4 protein, human; D008024:Ligands; D010455:Peptides