Regulation of interleukin 4 receptors on human T cells

Human recombinant interleukin 4 (IL-4) was modified with biotin-N-hydroxysuccinimide and used to examine the expression of human IL-4 receptors (IL-4R) on activated peripheral blood T cells by flow cytometry. Freshly isolated T cells expressed only a low level of IL-4R which remained unchanged when cells were cultured in the absence of stimuli. In the presence of IL-4, IL-7, phytohemagglutinin A (PHA), or immobilized CD3 mAb the intensity of biotinylated IL-4 staining increased approximately 2-fold on the majority of cells. A combination of mitogen with either IL-4 or IL-7 caused an increase in receptor expression over that seen in the presence of mitogen alone. IL-2 alone failed to induce IL-4R, although it was able to induce a significant increase in receptor expression on T cells co-cultured with PHA or CD3 mAb. Flow cytometric analysis of purified T cell subsets confirmed that the up-regulation of IL-4R occurred on both CD4+ and CD8+ subpopulations. Two-color staining of T cells activated with PHA and IL-7 revealed that this increase in IL-4R expression occurred almost exclusively on cells expressing the p55 IL-2Ra subunit, although a significant number of cells expressing p55 do not express IL-4R. Analysis of IL-4R expression by this flow cytometric technique was substantiated by 125I-labeled IL-4 binding data and Northern blot analysis of IL-4R mRNA levels, suggesting that use of biotinylated human IL-4 for ligand binding and its detection by flow cytometry provides a very sensitive method for the study of IL-4R regulation.