| Abstract: | Activated T cells express at least two distinct affinity classes of interleukin-2 (IL-2) receptors. The number of low-affinity receptors per cell is normally 10-30 times greater than that of the high-affinity receptors, and the difference in the dissociation constant between the two classes of receptors is in the order of 1,000-fold. In this report normal human T cells are used in a cellular system in which the number of low-affinity receptors can be manipulated. It is demonstrated that a cell population could be achieved with such low levels of low-affinity IL-2 receptors that almost half of the surface pool of anti-IL-2 receptor antibody (anti-Tac) binding sites represented high-affinity receptors. By using this cellular system it was possible to show that anti-Tac recognizes both receptor classes with similar affinity and that IL-2 inhibits Tac binding to both receptor classes in a competitive fashion. Tac antigens were purified from surface 125I-labeled cells expressing high levels of high-affinity IL-2 receptors, but low levels of the low-affinity receptor class, and this preparation was compared with another pool of Tac antigens obtained from cells expressing the normal 10- to 20-fold excess of low-affinity IL-2 binding sites over high-affinity IL-2 receptors. Biochemical characterization by peptide mapping by limited proteolysis and two-dimensional gel analysis revealed that these distinct preparations of Tac antigens were indistinguishable.(ABSTRACT TRUNCATED AT 250 WORDS) |
