Increased binding of IL-2 and increased IL-2 receptor mRNA synthesis are expressed by an NK-like cell line in response to IL-1.

An NK-like cell line (YTN10 cells) was stimulated with IL-1, and the IL-2R, as detected by flow cytometry analysis using fluorescein-labeled anti-IL-2R (Tac) antibody, increased displaying a dose-response curve in the shape of an inverted "U." This was associated with increases in 1) the number of high affinity binding sites for IL-2 (Kd approximately 45 pM) which increased from 1270 to 4220 sites per cell, and 2) the number of binding sites for anti-Tac antibody, which increased from 999 to 6763 sites per cell. They were both detected by using radiolabeled ligand-binding methods which are one to three orders of magnitude more sensitive than flow cytometry analysis. No binding sites with low affinity for IL-2 could be detected on untreated or treated cells. However, a change was noted in the number of IL-2 binding sites with intermediate affinity (Kd approximately 1000 pM), which increased from 54,000 to 67,000 sites per cell. This binding affinity is equivalent to that of the p70 IL-2-binding protein detected on YT cells and on large granular lymphocytes by other investigators. This suggests that the increase in the Tac peptide was the limiting factor in the combination of the Tac and p70 components to form the high affinity IL-2R. The corollary is that all new Tac molecules were incorporated into these R. The IL-1 treatment also induced an increase in production of Tac mRNA as detected by Northern blots. Comparison of the relative amounts of Tac mRNA by dot blots verified the quantitative difference between treated and untreated cells. These data demonstrate that the IL-1-induced positive regulation of the Tac protein and high affinity IL-2R on YTN10 cells may operate at the level of gene transcription.