Interleukin 2 binding molecule distinct from the Tac protein: analysis of its role in formation of high-affinity receptors.
- 1 April 1987
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences
- Vol. 84 (7), 2002-2006
- https://doi.org/10.1073/pnas.84.7.2002
Abstract
Interleukin 2 (IL-2) receptors on activated T cells exist in high- and low-affinity configurations, both of which share a ligand-binding component known as the Tac protein. Although almost all binding of IL-2 to such cells was inhibited by an antibody to Tac, the predominant component of binding on the natural killer (NK)-like cell line YT was resistant to this reagent. The ligand-binding component on YT cells also differed from Tac in its affinity constant (Kd .apprxeq. 8.2 .times. 10-10 M vs. Kd .apprxeq. 1.1 .times. 10-8 M for low-affinity Tac sites) and in its susceptibility to inhibition by certain antibodies to IL-2. When the YT cells were stimulated in a manner that induced expression of the Tac protein, the IL-2 binding sites were converted to a high-affinity configuration (Kd .apprxeq. 1.8 .times. 10-11 M). Thus, the original binding component on unstimulated YT cells appeared to combine with Tac and IL-2 to produce a high-affinity receptor complex. Use of bifunctional crosslinking agents following ligand binding to unstimulated YT cells yielded covalent IL-2-receptor complexes of 83 and 90 kDa. These complexes were similar in size to those derived from high-affinity receptors on activated T cells and shared a similar fragmentation pattern upon proteolysis. These results demonstrate the existence of a second IL-2 binding component in addition to the Tac protein and suggest that this component combines with Tac and IL-2 to form high-affinity receptor sites.Keywords
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