Lectin-binding proteins as potent mitogens for B lymphocytes from nu/nu mice

It was found that lectin-binding protein (LB) from leguminosae seeds can serve as mitogens B lymphocytes from athymic nu/nu mice. Most of the experiments were performed using a LB from Vicia faba as this was the most potent mitogen among all LB tested. When mixed B and T lymphocyte populations were stimulated by LB a bell-shaped dose-response curve resulted which is also characteristic of the corresponding lectins; LB, however, act at much higher concentrations than the lectins. In control experiments, using lymphocytes from C3H/HeJ mice which have a genetic defect with respect to lipopolysaccharide responsiveness, the enhancement of DNA synthesis by LB was comparable to that observed with other strains. This indicates that stimulation by LB does not result from contamination by lipopolysaccharides. B lymphocytes from nu/nu mice were stimulated by LB as efficiently as mixed T and B lymphocyte populations whereas lectins per se had no effect on nu/nu lymphocytes. Cyclosporin A, a fungal metabolite, is known to specifically suppress T cell responses. Cyclosporin A did not influence the mitogenic activity of the LB from Vicia faba on unseparated spleen cells. Cell populations enriched for T cells (lymph node cells: nylon wool-passed or nylon wool-passed and anti-Ia plus complement-treated) responded poorly to LB, if at all, even in the presence of interleukin 2-containing supernatants.