Dextran sulphate selectively enhances interleukin-2-dependent cytotoxic T lymphocyte growth but not differentiation

We have recently observed that dextran sulphate (DxS) interacts with molecules responsible for terminal B-cell maturation. Since this property of DxS is most likely due to its anionic characteristics, we have investigated whether this molecule could also modulate the response of cytolytic T cells (CTL) to interleukin-2-conditioned medium (IL-2 CM). Our data demonstrate that DxS synergizes with IL-2 in supporting the clonal expansion of CTL. Using limiting dilution analysis, we were able to establish that DxS acts directly on IL-2 CM and not on the responding lymphocytes and that the synergism observed in the result of increases in both clone size and the frequency of CTL precursors. Finally, since we could also demonstrate that DxS selectively affects the growth- but not the differentiation-promoting activity present in IL-2 CM, our results lend further support to the notion that CTL growth and differentiation are mediated by distinct soluble products. The possible mechanisms by which DxS alters the property of CTL growth-supporting activity are discussed, together with the practical implication of our findings.