Lymphocyte adhesion molecules in autoimmune rheumatic diseases: basic issues and clinical expectations

Lymphocyte adhesion molecules are of crucial importance in (auto)immune and inflammatory responses in two ways: on the one hand they mediate the interactions between lymphocytes and vascular endothelial cells during extravasation and homing, and allow local retention by aiding adhesion to extracellular matrix components, and on the other they increase T cell-antigen presenting cell contact and deliver the necessary signals for effective T-helper and T-cytotoxic cell function. Aberrations in adhesive interaction between members of the three major families of adhesion molecules, namely between selectins and their carbohydrate ligands, integrins and their ligands, and between members of the immunoglobulin superfamily, may participate in a vicious circle ending in organ damage. Findings regarding the overexpression of a number of adhesion molecules in patients with autoimmune rheumatic diseases, which is induced at the sites of inflammation and autoimmune injury, probably as a result of cell activation, exposure to cytokines or other soluble mediators, are summarized in the present review. Specific aberrations in adhesion molecule expression confined to one particular disease have not yet been described. Increased levels of soluble forms of various adhesion molecules that have been found in the serum of these patients reflect cell activation and may have physiological in vivo effects by interfering with cell-cell interactions. Although circulating adhesion molecule measurements lack specificity, longitudinal studies may establish their clinical value in the monitoring or the prognosis of patients. Modulation of adhesion mechanisms is likely to play an important role in the treatment of autoimmune rheumatic diseases in the near future. Indeed, preliminary results in patients with long-standing, refractory RA treated with a monoclonal antibody to intercellular adhesion molecule-1 are promising. However, much more has to be learned regarding the function and significance of adhesion molecules in order to successfully apply research findings to the clinical setting.