Interleukin 2 binding molecule distinct from the Tac protein: analysis of its role in formation of high-affinity receptors.
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 approximately 8.2 X 10(-10) M vs. Kd approximately equal to 1.1 X 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 approximately 1.8 X 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.
D000906:Antibodies; D000936:Antigen-Antibody Complex; D000954:Antigens, Surface / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D007376:Interleukin-2 / Q000378:metabolism*; D007700:Kinetics; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000378:metabolism*; D015375:Receptors, Interleukin-2; D013601:T-Lymphocytes / Q000276:immunology*; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7
D000906:Antibodies; D000936:Antigen-Antibody Complex; D000954:Antigens, Surface; D007376:Interleukin-2; D011948:Receptors, Antigen, T-Cell; D011971:Receptors, Immunologic; D015375:Receptors, Interleukin-2; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7