Levels of the soluble forms of CD80, CD86, and CD83 are elevated in the synovial fluid of rheumatoid arthritis patients

The release of soluble forms of CD80 (sCD80), CD86 (sCD86), and CD83 (sCD83) provide a potentially powerful immunoregulatory mechanism. We therefore investigated the potential presence and relative levels of these molecules in the synovial fluid (SF) and serum of patients with rheumatoid arthritis (RA) and osteoarthritis (OA). Serum and SF levels were measured by enzyme-linked immunosorbent assay. Serum levels of sCD80, sCD86, and sCD83 in RA and OA patients were similar to those present in normal donor serum (NDS) and the SF of OA patients. In contrast, when compared with NDS and OA SF levels, almost all RA SF samples had elevated sCD83 levels (32/35, > 0.63 ng/ml) and a substantial proportion had elevated sCD80 (13/29, > 0.22 ng/ml) or sCD86 (16/33, > 2.31 ng/ml) levels. Analysis of matched pairs of serum and SF from RA patients demonstrated that the SF/serum ratio for sCD80 (95% CI = 1.7-3), sCD86 (95% CI = 1.5-3.1), and sCD83 (95% CI = 3.6-7.8) levels was > 1 in almost all patients. In conclusion, this study shows that the SF from almost all RA patients contain elevated levels of sCD83 and the majority of these samples also contain elevated levels of sCD80 and/or sCD86. These molecules may play a role in modulating immune responses within the rheumatoid joint.