Differential expression of the costimulatory molecules B7.1 (CD80) and B7.2 (CD86) in rheumatoid synovial tissue.

CD4+ T-lymphocytes require two signals to become activated--antigen receptor (TcR) occupancy and an antigen-presenting cell (APC)-derived costimulus. The latter may be provided by B7.1 (CD80) or B7.2 (CD86) on APC interacting with CD28 on T-cells. We have studied the expression of these costimulatory molecules in rheumatoid and osteoarthritic synovial membrane. Very few B7.1-positive cells were seen in synovial tissue from either established or early rheumatoid disease, or in rheumatoid arthritis (RA) or osteoarthritis (OA) synovia at arthroplasty. In contrast, B7.2 was readily detected in rheumatoid synovia, predominantly in the lining layer, in a pattern of expression that corresponded to the presence of CD68-positive macrophages. Only occasional B7.2-positive cells were seen in OA synovia. The presence of B7.2 but the relative lack of expression of B7.1 may be partly responsible for the observations of 'frustrated' T-cell activation or T-cell hyporesponsiveness in the rheumatoid synovium.