Alteration of cell cycle kinetics and immunoglobulin gene transcription as the result of multiple agonist stimulation of murine B cells.

Several laboratories have established that anti-IgM can inhibit polyclonal B cell activation by LPS or LPS/DxS. The use of intact anti-IgM results in an inhibition of both proliferation and differentiation, whereas F(ab')2 fragments inhibit only differentiation. Since signal transduction by both alpha-Ig's (intact and F(ab')2 fragments) is known to be mediated by PIP2 hydrolysis, we have investigated the effects of A23187 and PMA on LPS/DxS activation of splenic B cells. These agents mimic the second messengers generated as the results of PIP2 hydrolysis. As with intact alpha-IgM, either agent in conjunction with LPS/DxS resulted in an inhibition of proliferation as assessed by [3H]thymidine uptake. However, when proliferation was assessed by acridine orange (AO) staining and flow cytometric analysis, cells were observed to have entered cell cycle. This disparity between AO staining and proliferation was resolved by using BrDu/Hoechst quenching analysis and revealed a delay in cell cycle transit time as the result of multiple agent stimulation. Since both anti-IgM's result in the inhibition of differentiation, we also investigated the effects of these agents on differentiation normally observed with LPS/DxS alone activation of B cells. A23187 and PMA, either alone or in combination, were observed to result in a decrease in mRNA-encoding mu immunoglobulin of the 2.4-kb mRNA for secreted IgM.