Interleukin 4 is a pleiotropic cytokine produced primarily by activated T cells, mast cells and basophils. The diverse biological effects of IL-4 on a variety of cell types are mediated by the binding of IL-4 to specific cell surface receptors. As is the case with many other cytokines, the functional high-affinity receptor for IL-4 is a complex consisting of a ligand binding subunit ( alpha chain) and a second subunit ( beta chain) that can modulate the ligand binding affinity of the receptor complex. It has been shown that in certain cell types, the gamma chain of the IL-2 receptor is a functional component ( beta chain) of the IL-4 receptor complex.
cDNA clones for the ligand binding chain (IL-4 R) of both the mouse and human high affinity IL-4 receptors have been isolated. The human or mouse IL-4R is an approximately 140 kDa transmembrane protein containing an extracellular domain, a transmembrane domain, and a large cytoplasmic domain that is essential for IL-4 signal transduction. In addition to the cDNA clone encoding the full-length transmembrane protein, a second cDNA clone that arises from alternate splicing and that encodes a soluble secreted form of IL-4 R has been isolated from mouse cells, but not yet from human sources. A naturally-occurring soluble form of the IL-4 R has also been identified in mouse biological fluids and murine cell culture supernatants.
Native or recombinant murine soluble IL-4 R, as well as recombinant human soluble IL-4 R, can bind IL-4 with the same affinity as the membrane bound IL-4 R. Soluble IL-4 R is a competitive inhibitor of IL-4 and has been shown to neutralize effectively many IL-4-mediated responses both in vivo and in vitro.
