Isotype-specific human B lymphocytes that produce immunoglobulin E in vitro when stimulated by pokeweed mitogen

Normal human peripheral blood lymphocytes can be stimulated by PWM and T cells to produce IgE in vitro. Between 4% and 10% of circulating B lymphocytes were found to bear noncytophilic membrane IgE. In contrast, limiting diluton analysis of active B cell precursor frequency revealed that only about 1 in 50,000 B cells was responsible for the synthesis of IgE in vitro. Variation inthe precursor frequency was primarily responsible for differences in the amount of IgE produced in vitro by different individuals while the amount of IgE produced per precursor cell was relatively constant. B lymphocytes with surface IgM, IgG, or IgE were depleted. Depletion of IgE-bearing cells decreased IgE production 70% to 83% while IgM-bearing-cell removal lowered IgE synthesis by 59% to 72%. Dual removal of IgM- and IgE-bearing cells did not give an additive effect. IgE- and IgM-positive B cells showed enhanced IgE synthesis of 327% and 182%, respectively. The consequences of crosslinking different surface isotypes on subsequent IgE production were also assessed. Anti-epsilon treatment inhibited IgE production up to 68% while anti-mu treatment decreased it by up to 38%. Thus only a very limited subset of B lymphocytes is responsible for PWM and T cell-dependent IgE synthesis in vitro and those cells probably bear both surface IgE and IgM.