Activation pathways triggered by interleukin-4 in the human plasmacytoma cell line RPMI-8226 - Differences with resting B lymphocytes

The early events following the ligation of interleukin-4 (IL-4) to the plasmacytoma cell line RPMI-8226 were analysed as a model of action for this interleukin on differentiated cells of the B lymphocyte lineage. The addition of recombinant IL-4 to these cells resulted in an increase of the intracytoplasmic free calcium concentration [Ca²+]i, but in contrast to normal B cells, this increase was mostly due to a calcium influx rather than to a mobilization from endoplasmic reticulum stores. IL-4 was also found to trigger cAMP accumulation in RPMI-8226 cells, with kinetics similar to that which has been described for normal resting human B lymphocytes. However, in contrast to normal B cells, IL-4 did not increase CD23 membrane expression on RPMI-8226 cells. But after incubation with high concentrations of IL-4, soluble CD23 (sCD23/IgE-BF) could be detected in the supernatant of these cells. In addition, the proliferation of RPMI-8226 cells was only moderately affected by IL-4. The expression of the receptors for IL-6, a growth factor for plasma cells, was not modified upon incubation of these cells with IL-4. These results therefore suggest that terminally differentiating B cells, such as the RPMI-8226 cell line, share common pathways of activation by IL-4 with mature resting B lymphocytes, but differ in some respects.