Role of alpha chain-IL-2 complex in the formation of the ternary complex of IL-2 and high-affinity IL-2 receptor.
Using anti-Tac (anti-alpha chain) and 2R-B (anti-beta chain) antibodies, we studied the roles of IL-2 receptor subunits (alpha and beta chains) in the formation of IL-2 and high-affinity IL-2 receptor complex, which is the initial event of IL-2 induced T cell growth. High-affinity IL-2 binding which was undetectable in the presence of 2R-B antibody at 4 degrees C became fully detectable when examined at 37 degrees C, which explained the lack of inhibition by 2R-B antibody of IL-2-induced proliferation of the cells expressing high-affinity IL-2 receptor. We further studied the mechanism of the 'reappearance' of high-affinity IL-2 binding in the presence of 2R-B antibody. The addition of IL-2 to the cells preincubated with radiolabeled or fluorescence-labeled 2R-B antibody resulted in a marked decrease in the antibody bound to the cells expressing high-affinity IL-2 receptor at 37 degrees C. This decrease was blocked by the presence of anti-Tac antibody, which inhibited IL-2 binding to alpha chain, but not by 7G7/B6 antibody, which recognized a non-IL-2 binding site of its chain. Furthermore, the decrease in cell-bound 2R-B antibody was not due to the internalization of beta chain-2R-B antibody complex, because the amount of cell-bound Mik-beta3 antibody recognizing a non-IL-2 binding epitope of beta chain remained unchanged, nor to the inhibition by simple competitive binding of IL-2 molecules to beta chain as judged from comparative studies of competitive binding inhibition. Taking these data together, the reappearance of high-affinity IL-2 binding was considered to be caused by the replacement of 2R-B antibody at the IL-2 binding site of beta chain by alpha chain-mediated IL-2, and it was strongly suggested that alpha chain-IL-2 complex has a key role in the formation of the ternary complex of IL-2 and high-affinity IL-2 receptor. alpha chain may function as a dimension converter of IL-2 to effectively deliver IL-2 molecules to a relatively small number of beta chains in the dynamics of the formation of high-affinity IL-2 binding in T cells.
Kamio
M
M
First Division of Internal Medicine, Faculty of Medicine, Kyoto University, Japan.
Uchiyama
T
T
Arima
N
N
Itoh
K
K
Ishikawa
T
T
Hori
T
T
Uchino
H
H
D000911:Antibodies, Monoclonal; D001665:Binding Sites; D002455:Cell Division; D002460:Cell Line; D006801:Humans; D007376:Interleukin-2 / Q000378:metabolism*; D007700:Kinetics; D015394:Molecular Structure; D015375:Receptors, Interleukin-2 / Q000737:chemistry / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D007376:Interleukin-2; D015375:Receptors, Interleukin-2