Interleukin-4 enhances peritoneal B cell stimulation induced by phorbol ester.

The activation requirements of murine peritoneal B cells differ from those of conventional (splenic) B cells; in particular, peritoneal B cells are stimulated to enter S phase by phorbol ester, acting alone. This pathway was studied to assess the susceptibility of peritoneal B cells to regulation by T cell products. Three T cell supernatants enhanced phorbol myristate acetate (PMA)-induced peritoneal B cell stimulation. This enhancement was reproduced by recombinant interleukin 4 (IL-4), and IL-4-mediated enhancement was reversed by 11B11 anti-IL-4 antibody. Enhancement of S phase entry was dose dependent for IL-4 and required stimulatory concentrations of PMA. In addition, IL-4 in combination with PMA produced a marked increase in IgM secretion by peritoneal B cells cultured in vitro. Neither an enhancement of S phase entry nor an increase in IgM secretion was observed with splenic B cells similarly treated with IL-4 and PMA. These results suggest that IL-4 modulates the proliferative and differentiative responses of the unusual B cells that reside in the peritoneal cavities of normal mice.