Immunosuppressive activity of glycosphingolipids. Influence of serum factors on ganglioside inhibition of IL-4-dependent cell proliferation

Gangliosides have been shown to inhibit proliferation of the interleukin-4 (IL-4)-responsive cell line CT.4R. Kinetic analysis has revealed that gangl ioside GT1b is a competitive inhibitor of proliferation, while GM1 and GM3 show a mixed pattern of inhibition, i,e., exhibit more than one inhibition type. Contribution of the competitive cell inhibition for GM1 and GM3 depen ds on serum factors added: the higher is the percentage of FCS, the larger is the contribution of the competitive inhibition, The pattern of prolifera tion inhibition shown for GT1b does not depend on the FCS content. We have also studied the interaction of the recombinant IL-4 with fluorescent (anth rylvinyl-labeled) gangliosides GM1 and GM3 and lactosylceramide incorporate d into liposomes, Dissociation constants of the IL-4-ganglioside complexes have been determined; lactosylceramide does not interact with rIL-4. The K- d values for the lymphokine complexes with gangliosides support the conclus ion based on the kinetic analysis that IL-4 has a higher affinity for GM3 ( K-d = 5 nM) than for GM 1 (K-d = 0.28 mu M).