Lymphocyte adhesion through very late antigen 4: evidence for a novel binding site in the alternatively spliced domain of vascular cell adhesion molecule 1 and an additional alpha 4 integrin counter-receptor on stimulated endothelium.
Recent studies demonstrate that alternative splicing of mRNA from a single gene can produce two forms of vascular cell adhesion molecule 1 (VCAM-1): a six-immunoglobulin (Ig) domain form (VCAM-6D) and a seven-Ig domain form (VCAM-7D). Using a COS cell transient expression assay, we investigated whether VCAM-6D and VCAM-7D differ functionally in adhesion to the integrin VLA-4 (CD49d/CD29) on lymphoid cells. Binding of lymphoid cell lines and peripheral blood lymphocytes was completely blocked by VLA-4 monoclonal antibody (mAb) and one VCAM-1 mAb (4B9) to both VCAM-6D and VCAM-7D, whereas one VCAM-1 mAb (E1/6) completely blocked binding to VCAM-6D but only partially inhibited binding to VCAM-7D. We conclude that there is one VLA-4 binding site in the six Ig domains shared between VCAM-6D and VCAM-7D, and that the alternatively spliced domain 4 present in VCAM-7D provides a second VLA-4 binding site that is blocked by 4B9 but not the E1/6 mAb. We compared the inhibitory effects of anti-VCAM-1 and anti-VLA-4 mAbs on lymphoid cell adhesion to cultured human umbilical vein endothelial cells (HUVEC). The anti-VCAM-1 mAb 4B9 blocked the binding of PBL and lymphoid tumor cells to stimulated HUVEC better than the anti-VCAM-1 mAb E1/6. Because VCAM-7D is the predominant form of VCAM-1 expressed by stimulated endothelial cells, this difference in VCAM-1 mAb inhibition is attributed to lymphoid cell binding to VCAM-7D on stimulated HUVEC. Although the anti-VLA-4 mAb and anti-VCAM-1 mAb 4B9 equally inhibited PBL binding to stimulated HUVEC, mAb 4B9 inhibited the binding of two lymphoid cell lines significantly less than anti-VLA-4 mAb. Combination of 4B9 mAb with function-blocking antiserum to human fibronectin, a second known ligand for VLA-4, also failed to inhibit as much as anti-VLA-4 mAb. These findings suggest that adhesion of lymphoid cell lines through VLA-4 or other alpha 4 integrins may involve inducible counter-receptor(s) on endothelium distinct from either VCAM-1 or fibronectin. Time course experiments indicate that the fraction of alpha 4 integrin-dependent binding that can be blocked by anti-VCAM-1 mAb E1/6 rises and peaks within 2 h of tumor necrosis factor (TNF) stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)
Vonderheide
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RH
Department of Pathology, Harvard Medical School, Boston, Massachusetts.
Springer
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TA
D000818:Animals; D000911:Antibodies, Monoclonal; D001665:Binding Sites; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology*; D015815:Cell Adhesion Molecules / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000502:physiology*; D006801:Humans; D016023:Integrins / Q000378:metabolism*; D007700:Kinetics; D008214:Lymphocytes / Q000276:immunology*; D012326:RNA Splicing; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016029:Receptors, Very Late Antigen / Q000502:physiology*; D011994:Recombinant Proteins / Q000494:pharmacology; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D019010:Vascular Cell Adhesion Molecule-1
D000911:Antibodies, Monoclonal; D015815:Cell Adhesion Molecules; D016023:Integrins; D012333:RNA, Messenger; D016029:Receptors, Very Late Antigen; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D019010:Vascular Cell Adhesion Molecule-1