Fig. 4.

Digestion of human chromatin/anti-DNA IgG immune complexes and chromatin alone by rhDNase. Aliquots of chromatin alone in PBS (a), chromatin alone in systemic lupus erythematosus (SLE) serum (b), chromatin/anti-DNA ICs in PBS (c) and chromatin/anti-DNA ICs in SLE serum (d) were digested with increasing concentrations of rhDNase for 2 h at 37°C. The final chromatin concentration was 120 μg/ml DNA and the final anti-DNA IgG concentration was 180 U/ml by Farr assay. Digestion was stopped with EDTA, followed by overnight proteinase K digestion and agarose gel electrophoresis as described in Materials and Methods. The concentrations of DNase used, in ng/ml, are listed above each lane. Sizes of DNA size markers used, in base pairs (bp), are listed at the sides of each panel. (b,d) Undigestible ethidium-stained material at ∼1 kb has been observed in 11 individual SLE sera as well as pooled normal sera not containing added chromatin.