Heterogeneity of polyclonal B-cell activity in systemic lupus erythematosus.

We have examined the abnormal in vitro polyclonal B-cell activity observed in patients with systemic lupus erythematosus (SLE) using a staphylococcal protein A reverse hemolytic plaque assay. We have found the mean level of circulating immunoglobulin secreting cells (IgSC) in 30 SLE patients to be significantly elevated compared to that of normal subjects, although half of the SLE patients fell within the normal range. Cultures of SLE peripheral blood mononuclear cells (MC) stimulated with optimal or suboptimal doses of pokeweek mitogen (PWM) showed depressed IgSC responses as a group, compared to cultures of normal MC (p less than 0.005), although a fraction of patients had normal responses. In 11 of 30 SLE patients, IgSC were less numerous in stimulated than in unstimulated cultures, whereas all normal subjects showed augmented IgSC response in stimulated cultures (p less than 0.005). Impaired in vitro response was not due to (1) altered PWM induced activation, (2) aberrant kinetic response or (3) decreased survival in culture of SLE MC. Of note, altered IgSC responses did not appear to reflect antecedent in vivo B-cell activation. Numbers of circulating IgSC and PWM-induced IgSC were not correlated with clinical and serological indices of disease activity or status of corticosteroid therapy. These data indicate considerable heterogeneity with respect to polyclonal B-cell activity in SLE, and provide further insight into the relationships of in vivo and in vitro B-cell activation in patients with this disease.