Evidence for an association between CD23 and the receptor for a low molecular weight B cell growth factor

Low molecular weight B cell growth factor (BCGF) and a monoclonal antibody (MHM6) to the 45‐kDa, B lineage‐restricted, CD23 activation antigen (BLAST‐2; EBVCS) were found to be indistinguishable in their biological effects. Individually, both augmented DNA synthesis in activated, but not resting, B lymphocytes while no additional enhancement resulted from using the two agonists in combination. Furthermore, by increasing the expression of Tac, both MHM6 and BCGF promoted activated B cells to respond more vigorously to the late addition of recombinant interleukin 2. The presence of BCGF during B cell activations was found to down‐regulate the expression of the CD23 antigen while the coating of activated cells with MHM6 antibody diminished their capacity to absorb BCGF activity. The findings demonstrate that CD23 and a low molecular weight BCGF deliver a comparable growth‐promoting signal to activated B cells. A possible relationship between CD23 and the receptor for the low molecular weight BCGF is discussed.