Lupus erythematosus (LE) factors recognize both nucleosomes and viable human leucocytes.

The morphological LE test was completely inhibited by mixing LE-factor-positive sera with core mononucleosomes, the basic histone-DNA subunit of chromatin. Free DNA and free histones at physiological ionic strength were not inhibitory. The LE-factor-binding antigen was virtually completely regained by mixing DNA and the inner histones H2A, H2B, H3 and H4 in 2 M NaCl, followed by step dialysis to 0.15 M salt. Trypsin-digested core mononucleosomes did not inhibit the LE test, indicating that the antigenic site is located on the N-terminal region of the histones. Twenty-six out of twenty-seven LE-factor-positive sera contained antinuclear antibodies that cross-reacted with plasma membranes of viable leucocytes (referred to as X-ANA). By contrast, weak X-ANA activity was found in only two out of twenty-five LE-factor-negative sera with high ANA titres. Three LE-factor-positive sera were subjected to absorption with viable human leucocytes, which led to the complete disappearance of LE factor activity of all three sera. The data indicate that antibodies with LE factor activity recognize core mononucleosomes and a plasma membrane antigen of viable human leucocytes.