Purine enzyme levels in rheumatoid arthritis

We studied purine metabolism in rheumatoid arthritis (RA), adenosine deaminase (ADA), 5'-nucleotidase (5'NU) and purine nucleoside phosphorylase (PNP) activities by measuring the circulating mononuclear cells of patients with RA and healthy controls. Patients had significantly lower levels of ADA and 5'NU but not of PNP than controls. The decreases could not be related to age, antiinflammatory therapy, decreased percentages of T cells or imbalance between major T cells subsets. Differences in cell maturation or traffic could account for our observation. Alternatively, abnormalities of purine metabolism are not definitely excluded in RA if the lower enzyme activity is not sufficient to perform the metabolic steps.