|Ph.D Student||Zohar Yaniv|
|Subject||Chemokine/Cytokine Function of Soluble VCAM-1 Independent|
of Binding to VLA-4 and Its Role in the
Regulation of Inflammation and
|Department||Department of Medicine||Supervisor||Professor Nathan Karin|
|Full Thesis text|
Rheumatoid arthritis (RA) is a chronic inflammatory disorder affecting the joints. Adjuvant arthritis (AA) is an animal model for RA, induced in Lewis rats. The transmigration of leukocytes to the inflamed joint involves chemokines, cytokines and adhesion molecules. One most important interaction in this process is the firm adhesion of leukocytes to endothelium, mediated by the binding of Vascular Adhesion Molecule 1 (VCAM-1) on endothelial cells to its counter receptor Very Late Antigen 4 (VLA-4) on lymphocytes and monocytes. VCAM-1 is member of the Ig-SF, composed of seven immunoglobulin-like domains, where only domains 1 and 4 bind to VLA-4. Soluble VCAM-1, the result of proteolytic cleavage by TNF-α converting enzyme, was identified in several inflammatory disorders and was found chemotactic and angiogenic.
Several works have shown that in the course of autoimmunity, the self-tolerance to soluble, pro-inflammatory mediators is being broken, and an immune response, termed “beneficial autoimmunity”, is elicited against these mediators to neutralize their activity. This response can be augmented by DNA vaccines encoding for these mediators. We have found that in the course of AA, but not monoarthritis, rats mount an immune response against VCAM-1, measured by autoantibody titers to VCAM-1, which could be augmented by DNA vaccine encoding VCAM-1, and transfer of these antibodies suppressed AA but not Experimental Autoimmune Encephalomyelitis (EAE), in which the VCAM-1-VLA-4 interactions are crucial for the development of the disease. Based on these findings, we assumed that soluble VCAM-1 harbors pro-inflammatory properties that are VLA-4 independent in AA, but not EAE. We have generated DNA vaccines encoding for each domain to generate neutralizing antibodies. Only antibodies to domain 2 suppressed AA, whereas antibodies to the other domains did not influence the course of the disease.
To further investigate the role of domain 2 in AA, we have generated chimeric domains fused to the Fc of human IgG in mammalian expression system. Chimeric domain 2 attracted monocytes, but not lymphocytes, while the other domains showed no chemotactic activity to both cell lines. This migration could not be blocked by neutralizing monoclonal antibody to VLA-4, suggesting the involvement of a receptor other than VLA-4 in this process. Chimeric domain 2 also induced alterations in the phosphorylation state in monocytes. Based on our results, we propose here a novel mechanism by which soluble VCAM-1 attracts monocytes to the inflamed joint.