HIGH-AFFINITY INTERLEUKIN-2 RECEPTOR-ALPHA AND BETA CHAINS ARE INTERNALIZED AND REMAIN ASSOCIATED INSIDE THE CELLS AFTER INTERLEUKIN-2 ENDOCYTOSIS

High-affinity interleukin 2 (IL2) receptors on human T lymphocytes are multimeric complexes containing two IL2-binding polypeptides, alpha and beta-chains of 50-55 and 70-75 kDa, respectively, associated by noncovalent bonds. IL2 binds to high-affinity IL2 receptors on the surface of T lymphocytes, mediates cell growth, and is internalized. In this paper, we used a biochemical method to directly identify the receptors components internalized together with the ligand. I-125-IL2-receptor complexes were solubilized with the detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonate, and IL2-binding polypeptides were identified by cross-linking with disuccinimidyl suberate. Under such conditions, the noncovalent association between alpha and beta is maintained. After IL2 internalization, two complexes of about 70 and 90 kDa, IL2 cross-linked to alpha and beta, respectively, were found inside the cells. Both components were immunoprecipitated with either anti-alpha or anti-beta monoclonal antibodies. This shows that the alpha and beta-chains are found in an intracellular compartment after IL2 endocytosis, and remain associated as a ternary complex with IL2.