Soluble Human Interleukin–4 Receptor Is Produced by Activated T Cells under the Control of Metalloproteinases

Background: Soluble interleukin 4 receptors (sIL–4R) are present in biological fluids. In contrast to mice, in man no distinct mRNA coding for sIL–4R has been described, suggesting that human sIL–4R is exclusively produced by proteolytic cleavage of the cell surface receptor. It is not known whether human sIL–4R is actively produced during an immune response. Methods: Human purified T cells, CD4+, CD8+, CD45RA+ and CD45R0+ T cell subpopulations were activated in vitro. sIL–4R was determined in the supernatants, cell surface IL–4R was measured by flow cytometry and RT–PCR. Results: Recombinant sIL–4R inhibited IL–4–mediated proliferation and IL–5 upregulation by T cells. sIL–4R could be detected at low levels in supernatants of nonactivated T cells, but at high levels following TCR engagement. This response was paralleled by enhanced transcription and de novo synthesis of the human cell surface IL–4R. Both, activated naive CD45RA+ and memory CD45R0+ T cells, produced sIL–4R with long–lasting kinetics. IL–4 increased sIL–4R production by activated CD45RA+, but there was less of an increase by CD45R0+ T cells. In addition, interferon–γ enhanced sIL–4R production. Cycloheximide and dexamethasone inhibited sIL–4R production by activated T cells, but did not abolish constitutive release of sIL–4R. Phosphoramidon and 1,10–phenanthroline dose–dependently inhibited shedding of the IL–4R, even in nonactivated T cells. Conclusion: The production of human sIL–4R by T cells is regulated by TCR stimuli, IL–4 and IFN–γ and needs the activity of metalloproteinases. Thus, sIL–4R should be regarded as inducible and due to its IL–4–antagonizing activity an immunoregulatory molecule.