Characterization of the spontaneous DNA-synthesizing and/or IgG-secreting cells in peripheral blood from patients with systemic lupus erythematosus.

Characterization of the cells responsible for spontaneous DNA synthesis and/or IgG secretion in systemic lupus erythematosus (SLE) was undertaken by fractionation of the peripheral blood mononuclear cells (PBM). Each fraction was analyzed for its capacity to incorporate [3H]thymidine [( 3H]TdR) and secrete IgG without mitogen. The non-E rosette-forming cell (non-ERRC) fraction, which consisted of the surface immunoglobulin-positive [sIg(+)] cells and null cells, revealed a markedly increased spontaneous DNA synthesis (620.0 +/- 586.9 cpm) during the first hour of culture and an elevated spontaneous IgG secretion (8639 +/- 2630 ng/ml) during 9 days of culture. Of particular interest was the finding that both increased responses were conducted by the null cells; the null cell population had approximately a fourfold relative increase of [3H]TdR incorporation and a 60-fold relative increase of IgG secretion compared with the sIg(+) cell population. These results suggest that SLE patients have a small population of preactivated B-cell lineage cells, which lack sIg or have a very low density of sIg.