THE HUMAN LEUKOCYTE-ADHESION LIGAND, INTERCELLULAR-ADHESION MOLECULE-2 - EXPRESSION AND CHARACTERIZATION OF THE PROTEIN

The leukocyte cell-adhesion receptors, complexes of the cluster of differentiation antigen 11a with cluster of differentiation antigen 18 (CD11a/CD18), cluster of differentiation antigen 11b with cluster of differentiation antigen 18 (CD11b/CD18) and cluster of differentiation antigen 11c with cluster of differentiation antigen 18 (CD11c/CD18), are of major importance in several leukocyte functions. Previously a cellular ligand named intercellular-adhesion molecule 1 (ICAM-1) was identified, isolated and extensively characterized. Recently a second similar molecule, intercellular-adhesion molecule 2 (ICAM-2), was found by a functional DNA-cloning method. We have now synthesized the ICAM-2 DNA by the polymerase chain reaction (PCR), sequenced it, and transferred it into mammalian and bacterial expression vectors. A functional leukocyte-binding glycoprotein was obtained by transfection of COS-1 cells. A soluble protein-A-ICAM-2 fusion protein was made in Escherichia coli, purified and used for antiserum production. The antiserum precipitated a cell-surface protein with an apparent molecular mass of 55 kDa from ICAM-2 transfected COS-1 cells, leukocytes and endothelial cells, and inhibited leukocyte binding to transfected COS-1 cells. The bacterial fusion protein, lacking carbohydrate, specifically bound to leukocyte receptors.