Activation of murine B lymphocytes. III. Stimulation of B lymphocyte clonal growth with lipopolysaccharide and dextran sulfate.

Proliferation of single B cells was observed in response to the combination of LPS and DXS when spleen cells were placed into Terasaki plates at dilutions where the majority of wells containing cells contained one cell. Clones derived from a single cell exhibited varying morphologies and growth characteristics. Neither filler cells nor conditioned medium was required for these responses. Since isolated cells were stimulated, we conclude that B cells can be activated to clonal growth in the absence of accessory cells. Limiting dilution analysis showed that the frequency of cells responding to the combination of LPS + DXS was about 80% of the frequency of input B cells. When only LPS or DXS was present, the frequency of response was less than 25% and less than 5% of the input B cell frequency, respectively. This synergy in mitogenesis is consistent with previous kinetic and cytofluorometric analyses of mitogen-stimulated growth which have indicated that the combination of LPS + DXS removes requirements for cell interaction in growth induction and that B lymphocytes can be stimulated to growth directly.