A synergistic polyclonal response to dextran sulphate and lipopolysaccharide: immunoglobulin secretion and cell requirements.

The effects of the simultaneous addition of lipopolysaccharide (LPS) and dextran sulphate (DxS) were studied in a low-cell density culture system, which enables extensive cell proliferation and high immunoglobulin secretion. Using these two mitogens, a synergistic response was observed, with regard to both cell division and IgM secretion. However, only a very low IgG production could be detected. This was caused by the extensive cell proliferation, leading to suboptimal culture conditions. Thus, when the blasts were recultured at a lower density or when a lower initial cell concentration was used, a high IgG response was obtained. The synergistic response induced by LPS plus DxS was independent of T cells. Furthermore, no apparent need for phagocytic cells was found. Both the LPS- and the LPS plus DxS-induced activation led to a switch, preferentially to IgG2b and IgG3 secretion. This subclass pattern was not changed when the cultures were lacking functional T cells.