Kinetic study of interleukin‐2 binding on the reconstituted interleukin‐2 receptor complexes including the human γ chain

To gain an insight into roles of the interleukin‐2 (IL‐2) receptor γ chain in IL‐2 binding mechanisms, we examined association and dissociation rate constants for IL‐2 binding with a series of fibroblastoid L929 cell lines expressing IL‐2 receptor complexes reconstituted by transfection with the α, β and γ genes. The association rate constant (k) with the αβγ complex on L cells was fourfold larger than that with the αβ complex on L cells, and the dissociation rate constant (k') was one fifth of that with the αβ complex. These results indicate that the γ chain is involved in both mechanisms by which IL‐2 associates with and dissociates from receptors, resulting in the generation of the high‐affinity IL‐2 receptor along with the α and β chains. During the course of this study, we found that the IL‐2 dissociation from αβγ complex on lymphoid cells was a lot slower than that from the αβγ complex on fibroblast cells. A similar difference was observed with the βγ complex. These observations may indicate functional and constitutional differences of the high‐ and intermediate‐affinity IL‐2 receptor complexes between lymphoid and fibroblastoid cells.