Interferons (IFNs) are glycoproteins produced by virtually all nucleated cells in response to viral infection, but particularly by lymphocytes (IFN-γ), lymphoblasts (Type I IFNs), and fibroblasts (IFN-β). Type I interferons (IFN-α from leukocytes; IFN-β from fibroblasts) are produced early in viral infection. IFN-γ (Type II) is produced by T-lymphocytes and NK cells. Thus all of these cell types contribute to interferon production.