Blood and Blood Products:

• Interferons


  The first family of cytokines to be discovered
• Discovery of interferons


  1. Susceptible animal cells exposed to colonizing virus became resistant to other viruses

  2. Resistance induced by substance secreted by virally infected cells

  3. Substance named interferon
• Most species produce a whole range of interferons
• Interferons produced by humans

  • IFN-α
  • IFN-β
  • IFN-γ
• Interferons


  • Produced by a variety of different cell types
  • Exhibit a wide range of biological effects including: induction of cellular resistance to viral attack, regulation of most aspects of immune function, regulation of growth and differentiation of many cell types, sustenance of early phases of pregnancy in some animal species
• Leukocyte IFN


  IFN produced by human leukocytes in response to viral infections, initially used for clinical applications
• Immune-IFN


  pH-labile, non-virus-induced IFN produced by human T cells in response to mitogens and other foreign antigens
• Fibroblast-derived IFN (FIF)


  IFN identified and purified from fibroblasts following infection with virus or exposure to poly I:C
• Differences in crude human leukocyte IFN preparations were initially thought to be due to differing amounts of protein glycosylation, but subsequent amino acid analysis demonstrated 10 separate species of proteins</b>
• huIFN-a


  Major class of IFNs present in leukocyte or lymphoblastoid preparations
• huIFN-b


  IFN produced by fibroblasts
• huIFN-g


  Human immune IFN produced by activated T-lymphocytes
• Recombinant DNA technology


  Offered an economic method to produce large amounts of purified huIFNs
• The first biologically active interferon-like protein was produced in 1980 from bacteria, after sifting through 20,000 different genetic fragments
• The IFNs produced by these clones were designated a1 and a2
• Elucidation of the coding regions of IFN-a genes revealed that the heterogeneity in huIFN-a was not due to variations in glycosylation but was due to presence of distinct genes representing each expressed huIFN-a sequence
• The complete nucleotide sequences of huIFNa2 and huIFN-b were determined and cloned in 1981
• Unlike recombinant purified IFN-a2, which is species specific

  Buffy-coat huIFNa has broad species effects, producing responses in humans, bovines, and felines
• Mammalian IFNs are broadly classified into two structurally discrete categories

  • Type I IFNs (IFN-a, IFN-b, IFN-w, IFN-t)
  • Type II IFN (IFN-g)
• Type I and II IFNs


  • Differ in their primary amino-acid sequences, evolutionary relationships, receptor cross reactivity, sites of production, and inducibility
  • Nonetheless, type I and II IFNs induce overlapping sets of responsive genes and activate similar signaling cascades
• IFN-a and IFN-b receptors

  Require two subunits, IFNAR-1 and IFNAR-2, to elicit a cellular response
• IFN-g receptor


  Consists of two subunits, IFNGR-1 and IFNGR-2
• Signal transduction following binding of IFN-a or IFN-b to the receptor

  1. Specific tyrosine kinase tyk2, as well as tyrosine kinases JAK-1 and JAK-2, are phosphorylated

  2. Activated tyrosine kinases modulate signal-transducing peptides and induce the formation of ISGF3-a complex

  3. ISGF3-a complex translocates to the nucleus and binds to ISRE of DNA, resulting in transcription of IFN-specific genes
• Signal transduction following binding of IFN-g

  Forms STAT1 homodimer, which binds to GAS consensus sequences of DNA
• Other signaling cascades are also activated by IFNs, including phosphatidylinositol-3-kinase and mitogen-activated protein (MAP) kinase cascade
• Chronic hepatitis B


  Caused by hepatitis B virus (HBV), a DNA virus that affects about two billion people worldwide
• About 15% of infected individuals develop chronic infection, characterized by persistence of hepatitis B surface antigen (HBsAg) in serum and some degree of HBV replication
• Approximately 350 million people worldwide are chronic carriers of HBV, with the majority living in Asia and Africa
• In the United States approximately one million people have chronic HBV infection
• 2% of patients with chronic HBV infection develop cirrhosis each year, and 15% to 25% of patients with chronic HBV infection will die prematurely from cirrhosis or hepatocellular carcinoma
• Primary goal of treatment for chronic hepatitis B

  To convert patients from a high to a low level of HBV replication as evidenced by HBeAg seroconversion to anti-HBe with loss of detectable serum HBV DNA
• Interferon-a demonstrated durable HbeAg to anti-HBe seroconversion in 25% to 40% of patients receiving a 4 to 6 month course of therapy at a dose of 30 to 35 million units per week
• A meta-analysis of 15 clinical trials showed that HBeAg loss occurred in 33% of patients treated with interferon compared with 12% of untreated or placebo-treated controls
• Interferon therapy should be used with great caution in patients with decompensated cirrhosis since treatment may flare their disease, resulting in hepatic failure, and is often associated with significant cytopenia or infection
• Interferon therapy has been largely replaced by treatment with nucleoside analogues that appear to be at least as effective but can be given orally with few side effects
• Cytokines


  A diverse group of regulatory proteins or glycoproteins whose classification remains somewhat diffuse, acting as chemical communicators between various cells by binding to specific cell surface receptors and triggering intracellular signal transduction events
• Most cytokines act upon, or are produced by, leukocytes (white blood cells), playing a central role in regulating both immune and inflammatory function and in related processes such as haematopoiesis and wound healing
• In more than 30% of cases, HbeAg-to-anti-HBe seroconversion occurs, in almost 20%, and histologic improvement in more than half of cases
• Longer courses of lamivudine further increase the chance of seroconversion (28% at 2 years, 40% at 3 years, 48% at 4 years) but also result in a high likelihood of developing a YMDD mutation in the polymerase gene that confers lamivudine resistance
• Other potent antiviral agents for hepatitis B are in clinical trials and will continue to make interferon a less attractive therapeutic option