Increased spontaneous release of cytidine deaminase by polymorphonuclear neutrophils of patients with active systemic lupus erythematosus

Cytidine deaminase activity (CD) in the neutrophil culture supernatants (PMN SUP) of 27 patients with systemic lupus erythematosus (SLE) was measured using a spectrophotometric method. Compared with the controls (5.449±1.358 U/5 × 10⁶ PMN), the CD activity in the spontaneous culture supernatants of PMN was significantly increased in active (10.003±2.637 U/5 × 10⁶ PMN) but not in inactive (5.358±1.624 U/5 × 10⁶ PMN) SLE. However, after stimulation with N-formyl-methionyl-leucyl-phenylalanine (FMLP, 1 × 10^-7 M), the ratio of enzyme activity between stimulated and spontaneous PMN supernatants was decreased in active SLE (0.794±0.178) compared with normal controls (1.300±0.225). In contrast, the enzyme activity in the cytoplasm of either stimulated or non-stimulated PMN was not different among these three groups. These results suggest that CD of PMN is releasable and can be enhanced by chemotactic factor stimulation in normal PMN. The increased spontaneous release of CD by active SLE PMN is one of the indicators for the disease activity in these patients.