Dipeptidyl peptidase-IV in synovial fluid and in synovial fluid mononuclear cells of patients with rheumatoid arthritis

BackgroundDipeptidyl peptidase-IV (DPP-IV) enzymatic activity controls biological halftime of multiple local mediators. Its deregulation is associated with pathogenesis of several autoimmune diseases, including rheumatoid arthritis (RA). Although DPP-IV is the canonical representative of the group, a number of other proteins have been shown to have similar enzymatic activity. This study was aimed to identify the molecular source of DPP-IV activity in synovial fluid (SF) and fluid mononuclear cells (FMNC) in patients with RA and osteoarthritis (OA). In addition, the association of DPP-IV and the concentration of stromal cell-derived factor-1α (SDF), DPP-IV substrate, were evaluated.MethodsDPP-IV activity was measured by the kinetic fluorimetric method. The expression of studied molecules in FMNC and their concentrations in SF were assayed using flow cytometry and ELISA respectively.ResultsDPP-IV activity in SF, dominantly derived from the canonical DPP-IV, does not significantly differ between RA and OA. However, a significantly lower DPP-IV activity and expression in FMNC was found in RA as opposed to OA patients. Negative correlation between SDF concentration in SF and the relative amount of CD3+CD26+ cells was observed.ConclusionsWe report decreased presence of DPP-IV/CD26 in CD3+ FMNC in RA, which also may participate on impaired balance of SDF concentration in SF.