The suppressive effect of gangliosides upon IL 2-dependent proliferation as a function of inhibition of IL 2-receptor association.

Gangliosides inhibited the proliferation of mitogen-activated human peripheral blood lymphocytes and the IL 2-dependent growth of murine T cell lines and 5-day-old human PHA lymphoblasts. In the case of the murine cell lines and PHA lymphoblasts, most of the effect of gangliosides could be reversed by the addition of high levels of IL 2. In the case of freshly-stimulated mitogen blasts, however, the ganglioside-induced inhibition could not be reversed by increasing exogenous IL 2 levels. These results indicate that inhibition of proliferation by gangliosides can be divided into IL 2-reversible and IL 2-irreversible mechanisms, the latter of which were predominant during the initial stage of cellular activation. Inclusion of gangliosides in receptor binding assays for radiolabeled IL 2 indicated that the IL 2-reversible mechanism likely involved competition between gangliosides and the cellular receptor for the binding of IL 2. Gangliosides blocked binding of radiolabeled IL 2 to both the high and low affinity forms of the IL 2 receptor, and this effect was most noticeable when the gangliosides and IL 2 were preincubated before addition of the target cells. In contrast, treatment of cells with gangliosides had no effect on the affinity of the cellular IL 2 receptor if the free gangliosides were removed immediately before the binding assay. Gangliosides also blocked the binding of radiolabeled IL 2 to anti-IL 2 antibodies, supporting the notion that their inhibitory effect is mediated via a direct interaction with IL 2. Thus, one major mechanism by which gangliosides block the IL 2-dependent proliferation of activated cells is by the sequestering or inactivation of the IL 2 molecule. This effect is reversible with the addition of excess IL 2, which distinguishes it from other mechanisms of ganglioside-dependent inhibition operating during the cellular activation process.