HUMAN LYMPHOCYTE-B SUBSETS .1. IGG-BEARING B-CELL RESPONSE TO POKEWEED MITOGEN

The subset of B lymphocytes bearing surface IgG was purified from human spleen and blood using a fluorescence-activated cell sorter. This subset constituted .apprx. 15% of B lymphocytes. The remaining non-IgG-bearing B cells were also obtained for study. These 2 populations were examined for: their expression of other surface Ig isotypes; their ability to give rise to IgG- and IgM-secreting (plaque-forming) cells in a pokeweed mitogen (PWM)-driven culture system; and, their ability to proliferate in response to PWM stimulation. Apparently most IgG-bearing B cells also express surface IgM and IgD. Less than 15% had only IgG. The IgG-positive cells gave rise to both IgG and IgM plaque-forming cells when driven by PWM, and in fact were responsible for most of the total plaque response in both the IgG and IgM classes. The non-IgG-bearing B cells were depleted of both IgG and IgM responsiveness. The non-IgG-bearing B cell failure to give a strong response to PWM did not appear to be due to either accessory cell depletion or to any suppressive influence. Proliferation studies indicated that both the IgG-bearing and the non-IgG-bearing cells proliferated in PWM presence with a somewhat stronger proliferative response in the IgG-bearing cells. Apparently the IgG-bearing cell is not irreversibly committed to IgG production, but can also give rise to IgM-secreting cells, and human PWM-driven Ig secretory responses are predominately due to a numerically small B cells subset.