IL-4 is a 15–20 kD glycoprotein composed of 129 amino acids. IL-4 contains six cysteine residues that are all involved in intramolecular disulfide bridges. The secondary structure of IL-4 was shown to consist of a four-helix bundle with a unique up-up-down-down helix topology. The X-ray structure reveals that IL-4 is a highly compact and globular protein with a predominantly hydrophobic core.
Human IL-4 receptor (IL-4R) is found on T cells, B cells, mast cells, basophils, macrophages, fibroblasts, endothelial cells, hepatocytes, keratinocytes, stromal cells, and neuroblasts. IL-4 receptor is a heterodimer composed of an α-subunit, with IL-4-binding affinity, and the common...