Direct demonstration that the monoclonal antibody AMT-13 and interleukin 2 bind to the same molecule

125I-labeled surface molecules from mouse T lymphoblasts were fractionated by affinity supports coupled with recombinant interleukin 2 (IL2) and the monoclonal antibody (mAb) AMT-13. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis demonstrated that two molecules of approximately 55 kDa and of approximately 180 kDa were bound in both cases. Sequential precipitation and SDS-PAGE analysis of the precipitated molecules revealed that only the approximately 55-kDa molecule eluted from AMT-13 mAb support was rebound to IL2 affinity support. In addition, IL2 inhibited specifically the binding of 125I-labeled AMT-13 mAb to T lymphoblasts. Thus the results directly demonstrate that the a approximately 55-kDa cell surface molecule represents the IL2-binding protein and that the mAb AMT-13 reacts with this molecule.