Function of peripheral blood lymphocytes in patients with systemic lupus erythematosus. Part 2. Significance of null cells in B cell activation

Activation of B lineage cells in systemic lupus erythematosus(SLE) has been indicated by the synthesis of IgG without mitogenic stimulation. In the course of this study, a cell population in SLE peripheral blood which synthesized DNA spontaneously and which fractionated into a null cell population was noticed. It was found that cells responsible for hyperproduction of IgG without any stimulation in vitro belonged to the null cell population, not to the sIg(+) cell population. The data suggested that both spontaneous IgG production and DNA synthesis might be performed by the same cell population in SLE. To test whether or not secreted IgG was synthesized by preactivated SLE peripheral blood lymphocytes, these cells were stained with FITC-labeled anti-human Ig antibodies. Significantly more cytoplasmic Ig(+) staining in SLE cells than in normal cells was found. These observations suggest that there was a small group of cells of B cell lineage in the SLE peripheral blood which was stimulated to proliferate and differentiate into a sIg(-) plasmablast line able to secrete IgG