Partial agonist/antagonist mouse interleukin‐2 proteins indicate that a third component of the receptor complex functions in signal transduction.

Some mouse interleukin‐2 (mIL‐2) proteins with substitutions at residue Gln141 are unable to trigger a maximal biological response. The Asp141 protein induces the lowest maximal response. The Asp141 protein can weakly antagonize the biological activity of mIL‐2 and strongly antagonizes the biological activity of active mIL‐2 mutant proteins that have defects in interactions with the high affinity receptor. Residue 141 mutant proteins bind with reduced affinity to T cells expressing the high affinity IL‐2 receptor, yet bind normally to transfected fibroblasts expressing only the alpha and beta chains of the receptor. These results suggest that a third receptor component is important for both binding and signal transduction.