Activation of murine B cells with Salmonella typhimurium mitogen (STM), lipopolysaccharide (LPS), and dextran sulfate (DxS). I. Cell-cycle analysis and induction of cytoplasmic immunoglobulin.

There have been two recent reports concerning a B cell-specific mitogen that induces proliferation, but not differentiation of rat and human B cells. This mitogen, which is derived from Salmonella typhimurium (STM), appears to be providing the signals required for anti-immunoglobulin-treated (anti-Ig) B cells to enter cycle and divide, but may not be inducing responsiveness to B cell differentiation factors (BCDF). In this report, we have compared STM to the other known murine B cell polyclonal activators: lipopolysaccharide (LPS), dextran sulfate (DxS), and the combination of LPS/DxS. STM was the most potent stimulus of B cell proliferation as determined by uptake of 3H-thymidine, viable cell numbers and cell cycle analysis utilizing acridine orange (AO). STM did not induce significant proliferation of murine T lymphocytes. In addition, the proliferative effect of STM on B cells shows minimal, if any, macrophage dependence. However, in contrast to its effect on human and rat B cells, STM induces differentiation of murine B cells. The levels of cytoplasmic Ig induced by STM are equivalent or greater to those induced by LPS/DxS. Thus, in the murine system, STM will be useful as a polyclonal activator which induces proliferation and differentiation of the vast majority of the B cell population without stringent accessory cell requirements.