Reduced purine 5 '-nucleotidase activity in lymphocytes of patients with systemic lupus erythematosus: results of a pilot study

Objective-To investigate purine metabolism in patients with systemic lupus erythematosus (SLE) for possible abnormalities that might be related to the ir overall impaired immune function. Methods-This pilot study included 17 patients with SLE (2 men, 15 women). E nzyme activities of the purine enzymes 5'-nucleotidase (5'NT), purine nucle oside phosphorylase (PNP), and hypoxanthine-guanine-phosphoribosyltransfera se (HGPRT) were measured in peripheral blood mononuclear cells (PBMC) and a lso in fractions of T cells (differentiation antigen CD3+) (n = 12) and B c ells (CD19+) (n = 9). The activity of the thiopurine enzyme thiopurine-meth yltransferase (TPMT) was measured in red cell lysate. Routine blood tests a nd indices of disease activity were measured as well. Results were compared with those of healthy volunteers. Results-Compared with their controls, the female SLE patients had a more th an 50% reduced activity of 5'NT in the T cell fraction (p = 0.001) and in P BMC (p < 0.000). 5'NT activity was also lower in B cells, but this was not statistically significant. Enzyme activities did not correlate with indices of disease activity, disease duration or the B cell/T cell ratio and no in fluence of medication was found. Conclusion-Reduced lymphocyte 5'NT activity is a novel finding in SLE. Thes e results indicate that purine metabolism in SLE may be disturbed. Conseque nces of a low 5'NT activity may be an intracellular accumulation of (deoxy) purine nucleotides and a reduction of adenosine production. It is hypothesi sed that these factors may play a part in the overall impaired immune funct ion and in the chronicity of inflammation in SLE.