The genes encoding type I interferons (IFNs), which include 14 IFN-(alpha) genes, one IFN-(beta) gene, one IFN-w (also known as IFN-(alpha) II1) gene, and a number of IFN-w pseudogenes, are clustered on human chromosome 9. Interferons-(alpha) and -(beta) are cytokines that are widely known to induce potent antiviral activity. IFN-(alpha) and -(beta) exert a variety of other biological effects, including antitumor and immunomodulatory activities and are increasingly used clinically to treat a range of malignancies, myelodysplasias and autoimmune diseases. IFN-w is antigenically different from human IFN-(alpha), IFN-(beta) or IFN-(gamma), but is a component of natural mixtures of IFN species produced by virus-induced leukocytes or Burkitt's lymphoma cells. The type I interferon receptor (IFN-(alpha)R) interacts with IFN-(alpha), IFN-(beta) and IFN-w, and seems to be a multisubunit receptor.