Purification of human interleukin 2 to apparent homogeneity and partial characterization of its receptor.

Human interleukin 2, produced by phytohemagglutinin-stimulated peripheral blood lymphocytes cultured in the absence of serum, has been purified to apparent homogeneity with a two-step combination of affinity chromatography with Cibacron blue-Sepharose and gel filtration. The specific activity of the purified IL-2 was 620,000 U/mg of protein, with a total recovery of approximately 13% biological activity. Purified IL-2 stimulated lymphocyte proliferation at a concentration of 4.3 X 10(-10) M. IL-2 was radiolabeled with reductive methylation to a specific activity of 350 microCi/nmol. Binding studies with phytohemagglutinin-activated lymphocytes, known to express receptor for IL-2, identified a single population of approximately 21,000 receptors per cell with an equilibrium dissociation constant of 7.1 X 10(-10) M.