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). Cellular attachment to and migration into ST is one of the critical aspects of chronic inflammation. This study was undertaken to examine the tissue distribution of a broad spectrum of monoclonal antibodies (mAbs) containing tetraspan antigens (CD9, CD63, CD151), endothelial cell antigens (CD31, CD36, CD105, CD106, CD146), integrins (CD49a- f, CD29, CD41, CD51, CD61), CD39, CD98, CD99, CD143 and, CD147 supplied from fifth and sixth international workshops and conferences on human leukocyte differentiation antigens in a comparative manner in human OA and normal synovium. Ten primary OA patients and six normal individuals were included in this study. The average age of the patients was 65.0 +/- 8.3 years and the average age of the controls was 31.8 +/- 5.3 years. Sections were screened using an indirect immunoperoxidase method. Tetraspan antigens and CD98 presented rather unique staining pattern in OA synovium suggesting special roles for each antigen on the synovial lining layer (SLL). Endothelial cells and type A synoviocytes expressed CD31 and CD36 in OA, but only endothelium in normal subjects. Integrins presented a uniform staining pattern in both groups. There was a positive reaction in some of the ST stromal elements for CD143 in all specimens. In conclusion, human normal and OA synovium were comparatively reviewed by a broad spectrum of mAbs with special attention being given to their functional aspects. This data suggests a significant difference in antigenic phenotype of SLL cells in OA and ST not to be considered at a normal- like state in OA. The fact that their activation was independent of the degree of lymphocyte infiltration further emphasizes the possible central importance of SLL.