ANPEP and rheumatoid arthritis: RA synovial fluid contained an average of 1074.68±652.41ng/ml of CD13 that was associated with EVs with an activity of 13309.33±12061.47μM/hr, and 2236.71±902.68ng/ml of soluble CD13 with an activity of 14960.44±3739.09μM/hr.A significant difference was observed between the levels of CD13 (p = 0.039) and aminopeptidase activity (p = 0.012) in the soluble fractions of plasma compared to RA synovial fluid.