Interleukin-4 receptor
Function. This gene encodes the alpha chain of the interleukin-4 receptor, a type I transmembrane protein that can bind interleukin 4 and interleukin 13 to regulate IgE antibody production in B cells. Among T cells, the encoded protein also can bind interleukin 4 to promote differentiation of Th2 cells. A soluble form of the encoded protein can be produced by an alternate splice variant or by proteolysis of the membrane-bound protein, and this soluble form can inhibit IL4-mediated cell proliferation and IL5 upregulation by T-cells. Allelic variations in this gene have been associated with atopy , a condition that can manifest itself as allergic rhinitis, sinusitis, asthma, or eczema. Two transcript variants encoding different isoforms, a membrane-bound and a soluble form, have been found for this gene. Interactions of IL-4 with TNFα promote structural changes to vascular endothelial cells, thus playing an important role in tissue inflammation. The binding of IL-4 or IL-13 to the IL-4 receptor on the surface of macrophages results in the alternative activation of those macrophages. Alternatively activated macrophages (AAMΦ) downregulate inflammatory mediators such as IFNγ during immune responses, particularly with regards to helminth infections. IL4 signalling also determines the levels  of CD20 on normal and malignant B cells by activation the transcription factor STAT6. Interactions. Interleukin-4 receptor has been shown to interact with SHC1. Structure. The N-terminal (extracellular) portion of interleukin-4 receptor is related in overall topology to fibronectin type III modules and folds into a sandwich comprising seven antiparallel beta sheets arranged in a three-strand and a four-strand beta-pleated sheet. They are required for binding of interleukin-4 to the receptor alpha chain, which is a crucial event for the generation of a Th2-dominated early immune response.