Objective To investigate the expression and the adenosine-generating activity of the ecto-5'-nucleotidase CD73 on synovial fluid mononuclear cells (SFMC) and peripheral blood mononuclear cells (PBMC) from children with arthritis. Methods Given the role of CD73 protein in the production of anti-inflammatory adenosine which intersects with inflammatory biology, its expression on lymphocytes was determined by flow cytometry. The CD73 AMPase activity of PBMC and SFMC was measured by HPLC. The effects of cell activation on CD73 expression were examined by in vitro culture of PBMC. Results CD8+ and CD19+ synovial lymphocytes from patients with juvenile idiopathic arthritis (JIA) expressed decreased levels of CD73 compared to both paired JIA PBMC and those from healthy controls. When comparing percentages of CD73+ synovial fluid lymphocytes in the two clinical forms of oligoarthritis, those with extended oligoarthritis showed lower CD73 expression compared to patients with the milder form of disease. Synovial CD8+ T cells had a lower ability to produce adenosine from Etheno-AMP compared to CD8+ PBMC. T cell activation through the TCR of CD8+CD73+ cells and B cell activation through TLR9 resulted in reduced expression of CD73. This downregulation occurred on dividing cells. Conclusion These data show that low CD73 expression on T and B cells in the inflammatory site is related to cell proliferation and is correlated with the clinical severity of oligoarticular JIA. The decreased CD73 expression on SFMC in turn results in reduced adenosine production, which would lead to decreased potential for anti-inflammatory activity
