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 f or this interleukin on differentiated cells of the B lymphocyte lineag e. The addition of recombinant IL-4 to these cells resulted in an incr ease of the intracytoplasmic free calcium concentration Ca2+!i, but i n contrast to normal B cells, this increase was mostly due to a calciu m influx rather than to a mobilization from endoplasmic reticulum stor es. IL-4 was also found to trigger cAMP accumulation in RPMI-8226 cell s, with kinetics similar to that which has been described for normal r esting human B lymphocytes. However, in contrast to normal B cells, IL -4 did not increase CD23 membrane expression on RPMI-8226 cells. But a fter incubation with high concentrations of IL-4, soluble CD23 (sCD23/ IgE-BF) could be detected in the supernatant of these cells. In additi on, the proliferation of RPMI-8226 cells was only moderately affected by IL-4. The expression of the receptors for EL-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 or activ ation by IL-4 with mature resting B lymphocytes, but differ in some re spects.