IgG subclass potential of surface IgM-negative and surface IgM-positive human peripheral blood B cells

To examine the IgG subclass potential of B cells at various stages of maturation, human peripheral blood B cells were separated into surface IgM-positive (sIgM+) and surface IgM-negative (sIgM-) cells by panning techniques and cultured with pokeweed mitogen, LPS, or Epstein-Barr virus. At the end of 7 days, cells were harvested, counted, spun onto slides, fixed, and stained with subclass-specific monoclonal antibodies. In all experiments with all mitogens, there was an enrichment of IgG2 plasma cells in sIgM+ cultures compared to the sIgM- cultures (P less than 0.0001). In the Epstein-Barr virus-stimulated cultures there was also a statistically significant enrichment for IgG3 in the sIgM+ cultures (P less than 0.01). In contrast, sIgM- cultures were always enriched for IgG1 plasma cells (P less than 0.0001). In the pokeweed mitogen-stimulated cultures, the sIgM- cultures also contained a higher proportion of IgG4 plasma cells than did the sIgM+ cultures (P less than 0.01). These results demonstrate that the IgG subclass potential of immature, surface IgM-positive precursors of IgG plasma cells differs from that of more mature surface IgM-negative precursors.