Glycophorin A interacts with interleukin-2 and inhibits interleukin-2-dependent T-lymphocyte proliferation.

Sialoglycolipids shed by tumor cells have been implicated in tumor-induced inhibition of T-lymphocyte responses to interleukin-2 (IL-2). In the present study, we have used glycophorin A, the major sialoglycoprotein of the human erythrocyte membrane, to investigate whether shedding of glycoproteins might also contribute to immunosuppression. Glycophorin A inhibited IL-2-stimulated proliferation of the IL-2-dependent cell lines HT-2 and CTLL-2 in a dose-dependent manner. Time course studies on synchronized cell populations indicated that the glycoprotein acted early in the activation process. On the other hand, glycophorin A had essentially no effect on IL-1-mediated stimulation of the IL-1-sensitive thymocyte cell line EL-4 NOB-1. Gel filtration FPLC demonstrated that IL-2 was able to bind to glycophorin aggregates under physiological conditions. Reconstituted vesicles containing glycophorin were also shown to bind IL-2. In addition, both soluble glycophorin aggregates and lipid vesicles containing glycophorin blocked binding of IL-2 to high-affinity cellular IL-2 receptors. Taken together, these results suggest that shedding of tumor sialoglycoproteins with oligosaccharide chains similar to glycophorin A might contribute to negative modulation of IL-2-mediated immune responses.