Activation of murine B cells. II. Dextran sulfate removes the requirement for cellular interaction during lipopolysaccharide-induced mitogenesis

Analysis of murine spleen cell growth at various initial cell densities suggested a requirement for cell interaction in some lipopolysaccharide (LPS)-induced B-cell proliferation. B-Cell mitogenesis by LPS did not exhibit single-hit kinetics. In addition, the proportion of cells demonstrating increase in cell size and transcriptional activity induced by LPS alone decreased with decreasing cell density. Dextran sulfate (DXS), a B-cell mitogen also described as requiring accessory cells for its mitogenic activity, was found to act synergistically with LPS in the induction of B-cell proliferation. Furthermore, the addition of DXS to LPS removed requirements for cell interaction in B-cell mitogenesis. As a consequence, the proportion of cells activated by the combination of LPS and DXS did not decrease as the initial cell density decreased.