Murine interleukin‐2 receptor subunits differentially detected with anti‐interleukin‐2 monoclonal antibodies

Cross‐linking of radioiodinated interleukin‐2 to murine CTLL‐2 cells enabled detection of 70 kDa, 85 kDa and 105 kDa complexes of IL‐2 and its binding proteins under the high‐affinity binding condition. A series of anti‐interleukin‐2 monoclonal antibodies (L15, L20, L23, L34, and L61) were tested for their activity to immunoprecipitate these cross‐linked complexes. L61, which had strong neutralizing activity, precipitated only the 70 kDa complex. L15, L20, and L34, which also had neutralizing activity, precipitated not only the 70 kDa complex but also the 85 kDa complex. L23, which had practically no neutralizing activity, precipitated the 105 kDa complex as well as the 85 kDa complex. These results suggest that there are at least three distinct receptor binding sites for each receptor subunit on the interleukin‐2 molecule, which are discernible by these monoclonal antibodies and that the 105 kDa complex may play a significant role in the formation of the high‐affinity receptor complex and the signal transduction.