Substrate competition in systemic lupus erythematosus: Clinical relevance

In an attempt to determine additional serologic correlates of lupus glomerulonephritis, 32 patients with systemic lupus erythematosus (SLE) and positive DNA binding were divided into three groups on the basis of six parameters: biopsy, urine sediment, creatinine clearance, proteinuria, C′_H100 or C₃, and anti-DNA binding. The three groups were: Group Ia, active renal disease; Group Ib, inactive renal disease; Group II, no renal disease. Samples of 42 sera from these patients, as well as samples from 10 normal controls, were assayed for their ability to inhibit the action of bovine pancreatic DNase on ¹²⁵I-labeled DNA (substrate competition). The mean levels of DNase activity for the groups were as follows: Group Ia, 9.42 ± 1.19 (SEM); Group Ib, 16.89 ± 1.09; Group II, 22.71 ± 1.74. The mean values for Group Ia and either of the other two groups were significantly different at the P < 0.001 level. Additional correlations were drawn between counterimmunoelectrophoresis for detection of precipitating antibody to DNA (C.I.E.) and DNase inhibition. The combination of high DNase inhibition and negative C.I.E. was highly predictive for SLE glomerulonephritis. This test may prove useful as an additional prognostic tool to determine which patients with SLE and positive anti-DNA binding will go on to get renal disease.