ABSTRACT
Fragments of intercellular adhesion molecule 1 (ICAM- 1) containing only the two most N terminal of its five immunoglobulin SF domains bind to rhinovirus 3 with the same affinity and kinetics as a fragment with the entire extracellular domain. The fully active two-domain fragments contain 5 or 14 more residues than a previously described fragment that is only partially active. Comparison of X-ray crystal structures show differences at the bottom of domain 2. Four different glycoforms of ICAM- 1 bind with identical kinetics.
Subject(s)
Intercellular Adhesion Molecule-1/chemistry , Rhinovirus/physiology , Antibodies, Monoclonal/immunology , HeLa Cells , Humans , Intercellular Adhesion Molecule-1/metabolism , KineticsABSTRACT
Rat mAbs were raised against murine intercellular adhesion molecule-2 (ICAM-2). Immune precipitation and purification reveal that the murine ICAM-2 glycoprotein is 55 kDa and is similar in size to human ICAM-2. ICAM-2 is expressed on a variety of leukocyte cell lines, including T and B lymphoma, mastocytoma, and macrophage lines. ICAM-2 is well expressed on endothelioma cell lines, and in contrast to ICAM-1, expression is not increased by inflammatory cytokines. One of the mAb to ICAM-2 partially or completely inhibits binding of cells expressing LFA-1 to purified ICAM-2, and binding of cells expressing ICAM-2 to purified LFA-1. The findings in the mouse are congruent with those in the human, suggesting functional conservation of ICAM-2 across species.
Subject(s)
Antigens, CD/chemistry , Cell Adhesion Molecules/chemistry , Animals , Antibodies, Monoclonal/immunology , Antigens, CD/immunology , Cell Adhesion , Cell Adhesion Molecules/immunology , Cell Line , Cloning, Molecular , Humans , Lymphocyte Function-Associated Antigen-1/metabolism , Mice , Protein BindingABSTRACT
Despite the identification and characterization of several distinct ligands for the leukocyte integrin (CD11/CD18) family of adhesion receptors, little is known about the structural regions on these molecules that mediate ligand recognition. In this report, we use alpha subunit chimeras of Mac-1 (CD11b/CD18) and p150,95 (CD11c/CD18), and an extended panel of newly generated and previously characterized mAbs specific to the alpha chain of Mac-1 to map the binding sites for four distinct ligands for Mac-1: iC3b, fibrinogen, ICAM-1, and the as-yet uncharacterized counter-receptor responsible for neutrophil homotypic adhesion. Epitopes of mAbs that blocked ligand binding were mapped with the chimeras and used to localize the ligand recognition sites because the data obtained from functional assays with the Mac-1/p150,95 chimeras were not easily interpreted. Results show that the I domain on the alpha chain of Mac-1 is an important recognition site for all four ligands, and that the NH2-terminal and perhaps divalent cation binding regions but not the COOH-terminal segment may contribute. The recognition sites in the I domain appear overlapping but not identical as individual Mac-1-ligand interactions are distinguished by the discrete patterns of inhibitory mAbs. Additionally, we find that the alpha subunit NH2-terminal region and divalent cation binding region, despite being separated by over 200 amino acids of the I domain, appear structurally apposed because three mAbs require the presence of both of these regions for antigenic reactivity, and chimeras that contain the NH2 terminus of p150,95 require the divalent cation binding region of p150,95 to associate firmly with the beta subunit.
