Description
IFN, also called Type II interferon, is a homodimeric glycoprotein containing approximately 21 to 24 kD subunits. The Human IFN gene, situated on chromosome 12, contains three introns; the four exons code for a polypeptide of 166 amino acids, 20 of which constitute the signal peptide. In contrast to IFN and IFN synthesis, which can occur in any cell, production of IFN is a function of T cells and NK cells. All IFN inducers activate T cells either in a polyclonal (mitogens or antibodies) or in a clonally restricted, antigen-specific, manner. IFN is produced during infection by T cells of the cytotoxic/suppressor phenotype (CD8) and by a subtype of helper T cells, the Th1 cells. Th1 cells secrete IL-2, IL-3, TNF and IFN, whereas Th2 cells mainly produce IL-3, IL-4, IL-5, and IL-10, but little or no IFN. IFN preferentially inhibits the proliferation of Th2 but not Th1 cells, indicating that the presence of IFN during an immune response will result in the preferential proliferation of Th1 cells. Type II IFN or IFN is a lymphokine that displays no molecular homology with type I IFN, but shares some important biologic activities. Specifically, IFN induces an anti-viral state and is anti-proliferative. In addition, IFN has several properties related to immunoregulation. (1) IFN is a potent activator of mononuclear phagocytes, e.g. IFN stimulates the expression of Mac-1, augments endocytosis and phagocytosis by monocytes, and activates macrophages to kill tumor cells by releasing reactive oxygen intermediates and TNF. (2) IFN induces or augments the expression of MHC antigens on macrophages, T and B cells and some tumor cell lines. (3) On T and B cells IFN promotes differentiation. It enhances proliferation of activated B cells and can act synergistically with IL-2 to increase immunoglobulin light-chain synthesis. IFN is one of the natural B-cell differentiation factors. (4) Finally, IFN activates neutrophils, NK cells and vascular endothelial cells