To elucidate the potential role of adhesion molecules in the pathogenesis of rheumatoid arthritis (RA), we stained specimens of synovial tissue from patients with RA and osteoarthritis (OA) with monoclonal antibodies against adhesion molecules using an immunohistochemical method. Positive staining with anti-ICAM-1 monoclonal antibody was detected on the synovial lining cells, the sublining cells and the capillary endothelial cells in the synovium from patients with RA, and, to a lesser degree, in that from patients with OA. The capillary endothelial cells from patients with RA intensively expressed both ELAM-1 and VLA-5α molecules, in contrast to that from OA patients. The intensity of both ICAM-1 and ELAM-1 on the capillary endothelial cells in RA synovium was comparable to disease activity and to the degree of synovial proliferation. A high density of expression of LFA-1α , VLA-4α and VLA-5α was observed on the mononuclear cells that infiltrated the RA synovium, especially in the lesions with aggregated mononuclear cells. The findings clearly demonstrated an up-regulation of the expression of adhesion molecules on synovial cells, capillary endothelial cells and infiltrated mononuclear cells in the synovial tissues of patients with RA. This enhanced expression of adhesion molecules may play an important role in the migration of mononuclear cells into the synovial tissues and thus perpetuate the inflammatory response in these tissues
