Keywords: CD98, 4F2, osteoarthritis, synovium, immunohistology


Introduction: Intercellular communication mediated by cell surface antigens is important in the maintenance of synovial tissue (ST) integrity. Chronic inflammation is a common feature of osteoarthritis (OA) and leukocytes invade the ST initiating a number of immunopathological processes. CD98 is a type II membrane glycoprotein which is known to be strongly expressed on activated cells, cell lines and malignant or transformed cells.
Patients and methods: The synovial lining layer and the underlying subsynovial tissue of 10 osteoarthritic patients and 6 normal individuals were evaluated immunohistologically for CD98 expression. STs were obtained from OA patients undergoing total joint arthroplasty and during diagnostic arthroscopy in the controls. Prepared sections were screened using an indirect immunoperoxidase method. Acid phosphatase staining was performed to identify the type A synoviocytes.
Results: CD98 was positive in the synoviocyte layer in almost all the lining layer of the normal ST. There was also a positive reaction in some of the ST stromal elements. A significant difference in antigenic phenotype of synovial lining cells in OA with the above mentioned activation marker was mainly present on the type A synoviocytes.
Discussion: Type A synoviocytes presented increased expression of CD98, suggesting that they are rapidly and fully activated. The fact that their recruitment was independent of the degree of lymphocyte infiltration further emphasizes the possible central importance of synovial lining layer in OA. The potential role of chronic cellular activation in the over-expression of CD98 in OA and ST, deserves further attention.