Studies of the in vitro activation and differentiation of human B lymphocytes. II. Optimization of activation by anti-immunoglobulin antibody bound to beads: analysis of the role of autocrine effects on B-cell proliferation and of T-cell help in B-cell differentiation.

We report experiments attempting to optimize the proliferative response of human B cells to rabbit anti-immunoglobulin antibody (RAHIg)-linked beads (anti-Ig beads). By choosing polyacrylamide beads of small size (3 micron) and coupling anti-Ig to them at high concentrations, beads were obtained which were both B-cell specific and more highly mitogenic than other than anti-Ig reagents and B-cell mitogens (SAC, protein A). Using these beads to activate B cells, the augmentation of the anti-Ig-induced proliferative response by added T-cell-derived growth factors was largely eliminated at high cell densities although the effect of these factors was still evident at low cell densities. However, when cultures were performed in round-bottom vessels which crowded the B cells together, the response to anti-Ig beads was independent of T-cell factors even at low B-cell densities, suggesting that normal B cells triggered by anti-Ig beads are able to maintain their own proliferation. In contrast to the proliferative response, even with the most potent anti-Ig bead preparations, no differentiation (Ig production or expression of terminal differentiation markers) was evident unless T-cell help was provided.