A monoclonal antibody to β, integrin (CD29) stimulates VLA-dependent adherence of leukocytes to human umbilical vein endothelial cells and matrix components

Abstract

The leukocyte β1 integrin receptor very late activation antigen-4 (VLA-4) (α4β1, CD49d/CD29) binds to vascular cell adhesion molecule-1 (VCAM-1) expressed on cytokine-activated endothelium. A mAb designated 8A2 was identified that stimulated the binding of U937 cells to CHO cells transfected with VCAM-1 cDNA but not endothelial-leukocyte adhesion molecule or CD4 cDNA. mAb 8A2 also rapidly stimulated the adherence of peripheral blood lymphocytes (PBLs) to VCAM-1-transfected CHO cells or recombinant human tumor necrosis factor-treated human umbilical vein endothelial cells. mAb 8A2-stimulated binding of PBL was inhibited by mAbs to VLA-4 or VCAM-1. Surface expression of VLA-4 was not altered by mAb 8A2 treatment and monovalent Fab fragments of mAb 8A2 were active. Immunoprecipitation studies reveal that mAb 8A2 recognizes β1-subunit (CD29) of integrin receptors. In contrast to mAbs directed to VLA-4 alpha-subunit (α4, CD49d), mAb 8A2 did not induce homotypic aggregation of PBL. Additionally, mAb 8A2 stimulated adherence of PBL and hematopoietic cell lines to purified matrix components laminin and fibronectin. This binding was blocked by mAbs to the VLA alpha-subunits α6 (CD49f), or α5 (CD49e) and α4 (CD49d), respectively. We conclude that mAb 8A2 modulates the affinity of VLA-4 and other leukocyte β1 integrins, and should prove useful in studying the regulation of β1 integrin function.