GANGLIOSIDES INTERACT WITH INTERLEUKIN-4 AND INHIBIT INTERLEUKIN-4-STIMULATED HELPER T-CELL PROLIFERATION

Gangliosides are potent immunosuppressive agents in vitro, and ganglio sides shed from tumours in vivo may play an important role in the esca pe of tumours from immune destruction. We have investigated the effect of gangliosides on interleukin-4 (IL-4)-mediated processes in the mur ine helper T-cell line HT-2. Various gangliosides inhibited IL-4-stimu lated DNA synthesis in HT-2 with IC50 values in the range 25-60 mu g/m l. However, the proliferation of four lymphokine-independent cell line s was unaffected by 500 mu g/ml gangliosides, as was the IL-1-stimulat ed secretion of IL-2 by EL-4 NOB-1 cells. Gangliosides were highly eff ective inhibitors when added to G(0)-G(1)-synchronized HT-2 cells duri ng the first 6 hr after IL-4 stimulation, indicating that they act ear ly in the IL-4 signalling pathway. High levels of exogenous IL-4 compl etely reversed inhibition of proliferation by gangliosides, which sugg ests that gangliosides compete with cellular IL-4 receptors for availa ble lymphokine. Receptor-binding experiments confirmed that gangliosid es blocked binding of [I-125]IL-4 to receptors on intact HT-2 cells in a dose-dependent fashion. Gelfiltration fast protein liquid chromatog raphy (FPLC) demonstrated that [I-125]IL-4 co-eluted with ganglioside micelles after co-incubation before chromatography, and an overlay tec hnique showed that IL-4 bound efficiently to gangliosides on thin-laye r chromatography plates. Taken together, these results indicate that g angliosides act as potent suppressors of IL-4-dependent processes in l ymphocytes, and that their mechanism of action involves direct interac tion with IL-4, thus preventing IL-4 binding to high-affinity IL-4 rec eptors. This information helps to explain the diverse immunosuppressiv e actions reported for gangliosides, both in vitro and in vivo.