Activity and expression of dipeptidyl peptidase IV on peripheral blood mononuclear cells in patients with early steroid and disease modifying antirheumatic drugs naive rheumatoid arthritis

Background: Dipeptidyl peptidase IV (DPPIV/CD26) plays an important role in T cell activation and immune regulation, however the role of this enzyme in early rheumatoid arthritis (eRA) has not been clearly defined. The aim of this study was to determine the serum activity of DPPIV, its expression on peripheral blood mononuclear cells (PBMC) and to examine possible correlations with disease activity (DAS28) in untreated patients with eRA. Methods: The study included 50 patients newly diagnosed with RA, who had not received any corticosteroid or disease modifying antirheumatic drugs (DMARD) therapy and whose conventional radiographs of hands and feet showed no structural damage. The control group consisted of 40 healthy volunteers. Also, 30 patients with chronic RA (cRA) were examined. The serum activity of DPPIV was determined by the direct photometric method, while expression of CD26 on PBMC was determined using flow cytometry. Results: Decreased DPPIV serum activity was detected in patients with eRA and cRA compared to the control group (p = 0.024, p < 0.0001, respectively). Although, the percentage of overall CD26+ white blood cells (WBC) was significantly decreased in eRA patients (p < 0.001), the percentage of CD26+ lymphocytes and monocytes and mean fluorescence intensity of CD26 on these cells in eRA patients showed no significant difference compared to healthy volunteers. DAS28 showed no significant correlation with CD26 expression or DPPIV serum activity, but a significant inverse correlation between the duration of symptoms and DPPIV serum activity was observed. Conclusions: Our results show that a decrease in DPPIV serum activity, but not CD26 expression, is present in an early stage of rheumatoid arthritis.