Murine B cell mitogens such as bacterial lipopolysaccharide (LPS), butanol-extracted water soluble adjuvant (Bu-WSA), dextran sulfate (DS), synthetic muramyl dipeptide (MDP), and its analog MDP-Lys (L18) do not show any mitogenic ability in vitro on human peripheral blood lymphocytes or mixed cell populations of purified T and B cells obtained from the lymphocytes in an ordinary culture system. However, these mitogens are capable of enhancing the mitogenic effect of concanavalin A (Con A) in the cultures.
In the presence of one of these mitogens, the activity of interleukin 2 (IL 2), but not interleukin 1, in the supernatants obtained from cultures containing Con A-stimulated T cell and B cell populations was higher than that of control cultures. The role of the newly produced IL 2 in the synergistic effect of the mitogens in human lymphocyte cell cultures was discussed.