Sharon, M., Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, United States
Gnarra, J.R., Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, United States
Leonard, W.J., Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, United States

Two proteins that specifically bind the T-cell growth factor interleukin 2 (IL-2) have been identified previously on the surface of T cels; these proteins have been designated IL-2Rα and IL-2Rβ for the α and β chains of the IL-2 receptor (IL-2R). The association of these independent binding proteins with each other on the surface of activated T cells correlates with the generation of high-affinity binding sites. These high-affinity sites transduce the major mitogenic signal of IL-2, yet the mechanisms of association of the α and β chains with each other as well as signal transduction in response to IL-2 are unknown. Cotransfection experiments of cDNAs encoding the α and β chains in T cells and fibroblasts have suggested functional requirements for other T cell-specific factor(s). We now provide biochemical evidence for a distinct 100-kDa protein that interacts with the α or β chains, or both, on the surface of the IL-2-dependent cell line CTLL-2 as well as activated murine splenocytes. This same 100-kDa protein is capable of being chemically cross-linked to 125I-labeled IL-2.