IFNAR1 is a member of the cytokine receptor superfamily which also includes receptors for interleukins, IFN gamma, ciliary neurotrophic factor, somatotrophin, erythropoietin, nerve growth factor, tumor necrosis factor, leukemia inhibitory factor, and oncostatin M. Some members of the family have an alpha chain with either low or high ligand binding affinity and at least one beta chain involved in signal transduction with either relatively low or no ligand binding affinity. Type I interferons, alpha and beta, induce a variety of effects on target cells including antiviral, antiproliferative, and immunomodulatory activities. The alpha and beta interferons compete to bind to a common cell surface receptor, while IFN gamma binds to a distinct receptor. IFNAR1 is very responsive to type I interferons and bind to IFN beta and IFN alpha subtypes. It is also functionally involved in signal transduction because of its association with the cytoplasmic tyrosine kinase JAK1. The type I interferons, alpha and beta, are produced by leukocytes (alpha subunits), fibroblasts (beta subtypes), lymphocytes (omega subtypes), and ruminant embryos (tau subtypes). Interferon receptors are generally found on most human cell types whatever their origin, even on cells poorly responsive to interferon. IFNAR1 is expressed on the cell surface in a variety of human cell lines.