Soluble and membrane-anchored forms of the human IFN-alpha/beta receptor

The recently cloned ligand binding component of the type I human interferon-alpha/beta receptor (IFN-alpha/beta R) and its soluble analogue (p40) were characterized. p40 is a potent inhibitor of type I IFNs and Antibodies directed against p40 completely block the activity of type I IFNs in human cells. These Antibodies immunoprecipitate cellular 102-kDa (major) and 51-kDa (minor) forms of IFN-alpha/beta R. We find that the 51-kDa IFN-alpha/beta R. Two types of cDNA clones were isolated and sequenced, a 1.5-kb cDNA coding for the transmembrane 51-kDa IFN-alpha/beta R and a 4.5-kb cDNA coding for p40. In addition to ligand binding, IFN-alpha/beta R is directly involved in signaling, because it becomes phosphorylated at Tyr residues on ligand binding and it is physically associated with the cytoplasmic tyrosine kinase JAK1.