KINETIC-STUDY OF INTERLEUKIN-2 BINDING ON THE RECONSTITUTED INTERLEUKIN-2 RECEPTOR COMPLEXES INCLUDING THE HUMAN GAMMA-CHAIN

To gain an insight into roles of the interleukin-2 (IL-2) receptor gamma 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 alpha, beta and gamma genes. The association rate constant (k) with the alphabetagamma complex on L cells was fourfold larger than that with the alphabeta complex on L cells, and the dissociation rate constant (k') was one fifth of that with the alphabeta complex. These results indicate that the gamma 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 alpha and beta chains. During the course of this study, we found that the IL-2 dissociation from alphabetagamma complex on lymphoid cells was a lot slower than that from the alphabetagamma complex on fibroblast cells. A similar difference was observed with the betagamma complex. These observations may indicate functional and constitutional differences of the high- and intermediate-affinity IL-2 receptor complexes between lymphoid and fibroblastoid cells.