The IL-4 Receptor — Signaling Mechanisms

Interleukin-4 (IL-4) is a multifunctional cytokine that is a member of the hematopoietin family1. Its structure consists of a bundle of four left handed α helices in which the first and second and the third and fourth helices are connected by long over hand loops2,3,4,5. IL-4 is produced by CD4+ T cells1 and by basophils and mast cells6 in response to receptor-mediated stimulation. It mediates its functions by binding to high affinity receptors expressed on a wide range of hematopoeitic and non-hematopoietic cell types7. The molecule defined as the IL-4 receptor (IL-4R) possesses an extracellular domain that is a member of the hematopoeitin-receptor family8. Its cytosolic domain is ~500 amino acids in length and lacks both endogenous tyrosine kinase and nucleotide-binding motifs9. The IL-4R does possess two acid rich regions and sequences homologous to the Box 1 region defined for the gp130 component of the IL-6 receptor10.