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Interferon Research 25
25
From:
Methods in Molecular Medicine, Vol. 116: Interferon Methods and Protocols
Edited by: D. J. J. Carr © Humana Press Inc., Totowa, NJ
2
Interferon Research
A Brief History
Myriam S. Kunzi and Paula M. Pitha
Summary
Interferons are the antiviral early inflammatory proteins produced in the cells in response to
the infectious agents. The characterization of the interferon genes, their expression, and their
function was advanced with the development of novel techniques in molecular and cellular
biology. Using genetically modified mice revealed the critical role of the interferons in innate
and acquired immune response. The critical steps and discovery that lead to the understanding
of the interferon system and its role in the antiviral immune response are summarized in this
chapter.
Key Words: Innate immunity; interferon; genes; receptors; clinical use; Toll receptors;
viruses.
1. Introduction
Interferon (IFN) was described in 1957 by Isaacs and Lindenmann (1) as an
antiviral protein synthesized by the cell in response to viral infection. The char-
acterization of this protein, its expression, and its function has been closely
linked to the availability of new methods and advances in cellular and molecu-
lar biology. Indeed, the isolation and detection of antiviral proteins synthe-
sized by infected cells was dependent on the development of techniques
enabling the cultivation of eukaryotic cells and the ability to use them for in
vitro viral replication. Later, the availability of specific antibodies and molecu-
lar biology techniques made it possible to recognize that IFN is represented by
a family of closely related, but distinct genes, to characterized IFN genes and
to purify IFNs, as well as produce sufficient amounts for clinical studies.
From the onset, researchers held the hope that IFNs could be used as a gen-
eral antiviral agent in the fight against viral infections, much like antibiotics
are used to control bacterial infections, thanks to their ability to inhibit a variety
of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) viruses. Unfortu-
26 Kunzi and Pitha
nately, the broad antiviral application has gone largely unfulfilled, mostly because
of the pleiotropic effects that IFNs exert on the cells. Nevertheless, the critical role
of IFNs in the antiviral immune response and cancer editing is just emerging
from studies using the genetically modified mice, and IFNs have been used in
the clinic for the treatment of selective viral infections and malignancies.
2. Purification and Characterization of IFNs
IFNs were initially identified as a group of proteins secreted by cells upon
viral infection and able to inhibit the growth of a wide range of unrelated
viruses. Whereas IFN did not appear to be virus-specific, it was recognized
to be species-specific. Human white blood cells were shown to produce IFN
upon infection, and they were regarded as a possible source of IFN for clinical
purposes. A number of experiments using actinomycin D at doses that inhib-
ited cell RNA synthesis, but not viral replication, demonstrated that IFN was a
product of the cell genome. The use of protein synthesis inhibitors further sug-
gested that IFN exerted its antiviral effect via the synthesis of one or more
proteins, which were the actual antiviral effectors. Quickly, it was recognized
as well that IFNs had properties able to regulate both cell growth and function.
IFN preparations available at that time, however, contained a number of impu-
rities, and the purification of small quantities of highly active IFN proved dif-
ficult. It was not until the advent of IFN-specific antibodies (2), which
permitted the isolation of IFN to near purity by column chromatography, that
the cell antigrowth effects of IFN could be confirmed.
The development of molecular biology techniques led to the detection mes-
senger RNA (mRNA) and genomic DNA in cells. The translation of interferon
mRNA in eukaryotic cell such as Xenopus oocytes and the high specific activ-
ity of IFN allowed for the detection of interferon proteins by their antiviral
activity in cell cultures (3).
3. Identification and Cloning of the IFN Genes
Once a standard assay for IFN mRNAs was established, several laboratories
nearly simultaneously cloned the IFN genes. The cloning of the IFN genes
brought two unexpected findings. First, it became clear that IFN is represented
by large number of cellular genes. These genes known as type I IFN, are repre-
sented by a family of 13 IFNA genes expressed in cells of lymphoid origin and
one IFNB gene expressed in a majority of infected cells (4–6). Although it was
believed for some time that there was at least one more IFN-β protein, IFN-β-
2, this protein was shown to be identical to IL-6. A single IFNW gene (7), with
sequence homology to IFNA, was found to be expressed in leucocytes, and
recently one IFNk gene, with sequence homology to both IFNA and IFNB,
was found to be expressed in keratinocytes and dendritic cells (8). Second, it
Interferon Research 27
was found that all type I IFN genes are nonspliced genes, and although their
expression shows cell specificity, all the genes are localized on the short arm
of chromosome 9 in human cells and on chromosome 4 in the mouse. All type
I IFNs are secreted proteins, although secretion of IFN-κ seems to be very
inefficient. IFN-β is modified by glycosylation, whereas the majority of IFN-α
are unglycosylated (9).
Finally, IFN-γ, or type II IFN, is encoded by a spliced gene localized on
chromosome 12 and has been shown to be synthesized selectively in cells of
the immune system, such as natural killer cells, CD4 Th-1 cells, and CD8 sup-
pressor cells (10,11). The ability to express IFN genes in bacterial expression
systems, coupled with affinity purification, provided sufficient amounts of IFN
proteins to study their specificity and ultimately provided sufficient amounts
for clinical studies
4. IFN Gene Regulation
The optimization of DNA transfection into eukaryotic cells has facilitated
the identification of the regulatory regions of the IFN genes. In this method,
genomic fragments localized at the 5' or 3' end of an IFN gene are cloned in
front of a reporter gene encoding an easily detectable protein, transfected into
cultured cells, and then their ability to induce expression of the reporter gene in
infected and uninfected cells is analyzed. These studies have identified a virus-
regulated element (VRE) in the promoter region of IFNA and IFNB, which
alone confer responsiveness to virus infection (12–14).
Studies of the molecular mechanism involved in the virus-mediated activa-
tion of type I IFN genes has brought about the discovery of IFN regulatory
factors (IRFs), a new group of transcriptional factors (15). The IRFs play a
critical role in the induction of type I IFN genes; chemokine genes; and genes
mediating antiviral, antibacterial, and inflammatory responses. Three of these
IRFs, IRF-3, IRF-5, and IRF-7, function as direct transducers of virus-medi-
ated signaling (16–18). In uninfected cells, these IRFs are expressed in the
cytoplasm, whereas in infected cells, they are activated by a C’ terminal serine
phosphorylation, which results in their translocation from cytoplasm to nucleus
(19). Recently, an IKK kinase, TBK-1, was shown to be responsible for the
phosphorylation and activation of IRF-3 and IRF-7 in infected cells, as well as
cells treated with double-stranded RNA (dsRNA)-polyIC (20,21). The target
of TBK-1 phosphorylation is a cluster of 4 serines in the carboxy terminus of
the IRF-3 polypeptide (22). In infected cells, the ubiquitously expressed IRF-3
mediates the induction of IFNB (23,24). Activation of this gene involves co-opera-
tive assembly of several transcription factors: nuclear factor (NF)κB, ATF-2/c-
june, IRF-3, and IRF-7 on the VRE of the IFNB promoter (25). This complex-
enhanceosome recruits two coactivators, acetyltransferase CBP/P300 and
28 Kunzi and Pitha
holoenzyme polII (26), whereas in the uninfected cells the IFNB promoter is
under a negative control (27). Most of the promoters of IFNA genes do not
contain an NFκB site, and their activation depends not only on IRF-3 but also
on IRF-5 or IRF-7, both of which were shown to be components of the IFNA
enhanceosome assembled on the VRE of IFNA genes (19,28). The chromatin
precipitation assay has permitted the detection of these enhanceosomes in liv-
ing cells. IRF-5 or IRF-7 expression in infected cells, unable to express IFNA
genes, restored the expression of a number of IFNA genes and IFN-α synthesis
(18,29). In most of the cells, expression of IRF-7 can be induced by interferon
induced transcriptional factor ISGF3 (30). Type I IFN genes can be therefore
generally divided into two groups: immediate-response genes, represented by
IFNB, which requires only IRF-3 for its induction and is therefore rapidly
induced in most infected cells, and late IFNA genes, which require IFN-acti-
vated IRF-5 or IRF-7. The fact that IFNB-null mice are unable to synthesize
IFN-α supports the dependence of IFNA expression on IFNB and the hypoth-
esis of a positive feedback operation in interferon mediated antiviral response
(31,32). However, the recently developed quantitative RT-PCR analysis of
RNA transcripts, as well as the sensitive detection of proteins by intracellular
immune staining, have shown that the high IFN-α-producing pDC2 cells, con-
sidered to be natural IFN-producing cells, express high levels of IRF-7 consti-
tutively in the absence of IFN synthesis (33). Thus the requirement for IFN-β
synthesis may not apply to these cells.
The discovery of toll receptors (TLRs) and their role in the innate immune
response has brought further unexpected findings. Three of these TLRs, TLR-
3, TLR-7, and TLR-9, are intracellular and double stranded RNA (dsRNA),
single-stranded RNA (ssRNA), and CpGDNA, respectively, are their ligands.
Furthermore, binding of the dsRNA to TLR-3 activates TBK-1 and results in
phosphorylation of IRF-3 and IRF-7 and the induction of type I IFNs. In con-
trast, TLR7 and TLR9 activate IRF-5 and IRF-7 but not IRF-3 (60,61).
It is noteworthy that synthesis of IFN-β also can be induced by the binding
of lipopolysaccharide to TLR-4 and that the induction proceeds through acti-
vation of TBK-1, and activation of IRF-3 and IRF-7 (34). These results indi-
cate that although the initial recognition of the infectious entity may be distinct,
the cellular response to bacterial or viral infection shows profound similarities.
However, none of these mechanisms could have been unambiguously estab-
lished, without the availability of genetically modified null mice with various
components of the TLR-mediated signaling pathway deleted.
Experiments with genetically modified mice have also indicated a role for
the members of the IRF family in the antiviral immune response. Thus, tar-
geted disruption of IRF-1 results in an increased sensitivity to viral infection, a
defect in the development of TH-1 responses and a resistance to apoptosis.
Interferon Research 29
IRF-4-null mice have a defect in both T- and B-cell maturation and, conse-
quently, defective immune functions (35). IRF-8-null mice show an increased
sensitivity to viral infection and a defect in the development of myeloid cells
and pDC2 subtype of dendritic cells that are high IFN-producing cells (36,37).
IRF-5-null mice show a profound defect in CPG DNA mediated responses (62).
Furthermore, because that the IRF-5 is a component of the p53-mediated
growth inhibitory and pro-apoptotic pathway (38) and, thus, a recently observed
antiviral activity of p53 may be mediated by IRF-5 (39).
5. IFN Receptors
Cellular receptors for type I IFNs and IFN-γ belong to the class 2 cytokine
receptor subfamily. In recent years, these receptors and the signaling pathways
they induce have been elucidated (40–42).
With varying degrees of avidity, all type I IFNs bind to the same receptor
made of two subunits, IFNAR1 and IFNAR2, of which there are a short and a
long variant, the result of differential mRNA splicing. IFN-α or INF-β induces
the association of IFNAR1 with the long variant of IFNAR2 and initiate a sig-
naling pathway involving the tyrosine kinases Tyk2, Jak1, and the ultimate
migration of activated transcription activators signal transducer and activator
of transcription (STAT)-1 and STAT-2 to the nucleus, where they bind together
with IRF-9 to a specific sequences (i.e., IFN-stimulated response elements)
within the promoters of IFN-stimulated genes (ISGs) and initiate their tran-
scriptional activation (43,44). The IFN-γ receptor also comprises two subunits
and the signaling pathway with which it is associated, involves Jak1, Jak2, and
STAT-1. Activated STAT-1 homodimers translocate to the nucleus and bind to
the γ-IFN activation sequence, culminating in the transcriptional activation of
specific genes (11).
Infection of genetically modified mice in which type I IFNR or IFNgR recep-
tor or critical component of the IFN signaling pathways had been deleted has
shown a central but not redundant role for type I and II IFNs in the host
response to infection. Thus, elimination of type I IFNR increases sensitivity
to infection by number of RNA viruses, whereas these mice are still resistant to
some bacterial infections (45,46). However, IFNGR-null mice show increased
sensitivity to microbial infections, as well as infection with some DNA viruses
such as HSV-1 and vaccinia (47).
6. IFN-Stimulated Genes
Although IFNs were initially identified by their antiviral properties, it was
recognized early on that the actual effector was not IFN itself, but one or sev-
eral proteins induced by IFN. Recently, microarray analysis of the cellular tran-
scripts induced in cells treated with IFN has estimated that IFN stimulates more
30 Kunzi and Pitha
than 300 ISGs with homology to genes involved in signaling, host defense,
immune modulation, transcription, translation, apoptosis, cell adhesion, anti-
viral and inflammatory responses, ubiquitination, and antigen processing
(48,49).
Not surprisingly, the most studied ISGs have been those with antiviral prop-
erties. The enzymes of the 2,5-oligosynthetase family (OAS-1 and OAS-2)
catalyze the synthesis of short oligoadenylates, which binds and activate
RNAseL, an enzyme that cleaves viral and cellular RNAs, thus inhibiting pro-
tein synthesis (50). DsRNA-activated protein kinase (PKR) phosphorylates the
translation initiation factor eIF2a, also resulting in the inhibition of viral and
cellular protein syntheses (51). More recently, PKR also was found to be
required for the activation of the transcription factor NFκB, a central actor in
inflammatory cytokine induction, immune modulation, and apoptosis (52). Mx
proteins are GTPases and this intrinsic activity is required for antiviral effect
(53). Mx proteins inhibit the replication of RNA viruses by either preventing
transport of viral particles within the cell, or transcription of viral RNA (54).
Another very interesting ISG is the RNA-editing adenosine deaminase that
converts adenosine to inosine, thus causing hypermutation of viral RNA genomes,
such as those of VSV and measles virus (55,56).
A number of ISGs encode chemokines such as interleukin-8 and monokine
induced by IFN-γ (Mig), which are involved in lymphocyte recruitment to the
site of infection and inflammation and the expression of genes encoding adhe-
sion molecules, such as ICAM-1 and CD-47, which are crucial for the ability
of leukocytes to adhere to, infected cells. Other ISGs encode transcription fac-
tors, most of them activators of transcription. ISG-15 is an ubiquitin-like pro-
tein, conjugated to cellular proteins and has been shown to target Jak-1, STAT-1,
and extracellular signal-regulated kinase-1 (57,58).
7. Clinical Uses of IFN
Recombinant IFN-α (rIFN-α; Roferon A; Intron A) and recently its
pegylated form (Pegasys), either alone or in combination with an antiviral
agent, are used in the treatment of chronic hepatitis C virus infection. Because
a number of ISGs are shown to have pro-apoptotic characteristics, there is also
a renewed interest in using IFN in the clinic to control malignancies. In the
past, Roeferon A–rIFNα has been used in the treatment of malignant melano-
mas, Kaposi’s sarcoma, genital warts, and hairy cell leukemia (59). Avonex
(IFN-β), produced in hamster cells, remains an essential element in the treatment
of multiple sclerosis (MS). Peripheral blood mononuclear cells isolated from
patients with active MS show decreased sensitivity to type I IFNs, decreased
ISG expression, and hypophosphorylation of STAT-1. In vitro treatment of
these cells with IFN-β overcomes these defects, thus suggesting that IFN-β
therapy may serve to restore normal levels of ISG expression in active MS.
Interferon Research 31
One should be mindful to remember however, that IFN therapy is accompa-
nied with burdensome side effects, presumably because of the large scope of
biological processes influenced by IFN and that, at best, it has been able so far
to only forestall but not halt the progression of the diseases mentioned here.
8. Conclusion
IFNs were the first early inflammatory proteins recognized to be produce in
cells in the response to viral infection. The characterization of IFN genes, their
regulation and functions, facilitated by the newly emerging techniques of molecu-
lar biology, opened a new insight into our understanding of the basic mecha-
nisms involved in the virus cells interaction and in the innate antiviral response.
The availability of genetically modified mice allowed them to study in vivo the
role of the IFN system in the antiviral response. These studies have revealed
the importance of the IFN system not only for the innate, but also for the ac-
quired immunity and pointed out to the existence of the cross talk between inter-
feron system and other cytokines. Furthermore, it has become obvious that the
role of IFN is not limited to the antiviral response, but that the IFN system
plays an important role in the regulation of cell growth, apoptosis, and matura-
tion of lymphoid cells. Understanding the mechanisms of the cellular effects of
IFNs and their interaction with other cytokines may also provide more realistic
approach to the clinical use of IFNs.
References
1. Isaacs, A. and Lindenmann, J. (1957) Virus interference. I. The interferon. Proc.
R. Soc. Lond. B. Biol. Sci. 147, 258–267.
2. Paucker, K. and Cantell, K. (1962) Neutralization of interferon by specific anti-
body. Virology 18, 145–147.
3. Reynolds, F. H., Jr., Premkumar, E., and Pitha, P. M. (1975) Interferon activity
produced by translation of human interferon messenger RNA in cell-free riboso-
mal systems and in Xenopus oocytes. Proc. Natl. Acad. Sci. USA 72, 4881–4885.
4. Derynck, R., Content, J., DeClercq, E., Volckaert, G., Tavernier, J., Devos, R.,
and Fiers, W. (1980) Isolation and structure of a human fibroblast interferon gene.
Nature 285, 542–547.
5. Kelley, K. A. and Pitha, P. M. (1985) Characterization of a mouse interferon gene
locus II. Differential expression of alpha-interferon genes. Nucleic Acids Res. 13,
825–839.
6. Nagata, S., Mantei, N., and Weissmann, C. (1980) The structure of one of the
eight or more distinct chromosomal genes for human interferon-alpha. Nature
287, 401–408.
7. Hauptmann, R. and Swetly, P. (1985) A novel class of human type I interferons.
Nucleic Acids Res. 13, 4739–4749.
32 Kunzi and Pitha
8. LaFleur, D. W., Nardelli, B., Tsareva, T., Mather, D., Feng, P., Semenuk, M., et
al. (2001) Interferon-kappa, a novel type I interferon expressed in human
keratinocytes. J. Biol. Chem. 276, 39765–39771.
9. Samuel, C. E. (1991) Antiviral actions of interferon. Interferon-regulated cellular
proteins and their surprisingly selective antiviral activities. Virology 183, 1–11.
10. Gessani, S. and Belardelli, F. (1998) IFN-gamma expression in macrophages and
its possible biological significance. Cytokine Growth Factor Rev. 9, 117–123.
11. Schroder, K., Hertzog, P. J., Ravasi, T., and Hume, D. A. (2004) Interferon-
gamma: an overview of signals, mechanisms and functions. J. Leukoc. Biol. 75,
163–189.
12. Goodbourn, S., Zinn, K., and Maniatis, T. (1985) Human beta-interferon gene
expression is regulated by an inducible enhancer element. Cell 41, 509–520.
13. Raj, N. B. K., Engelhardt, J., Au, W.-C., Levy, D. E., and Pitha, P. M. (1989)
Virus infection and interferon can activate gene expression through a single syn-
thetic element, but endogenous genes shown distinct regulation. J. Biol. Chem.,
264, 16658–16666.
14. Ryals, J., Dierks, P., Ragg, H., and Weissmann, C. (1985) A 46-nucleotide pro-
moter segment from an IFN-alpha gene renders an unrelated promoter inducible
by virus. Cell 41, 497–507.
15. Nguyen, H., Hiscott, J., and Pitha, P. M. (1997) The growing family of interferon
regulatory factors. Cytokine Growth Factor Rev. 8, 293–312.
16. Au, W.-C., Moore, P. A., Lowther, W., Juang, Y.-T., and Pitha, P. M. (1995)
Identification of a member of the interferon regulatory factor family that binds to
the interferon-stimulated response element and activates expression of interferon-
induced genes. Proc. Natl. Acad. Sci. USA. 92, 11657–11661.
17. Au, W. C., Moore, P. A., LaFleur, D. W., Tombal, B., and Pitha, P. M. (1998)
Characterization of the interferon regulatory factor-7 and its potential role in the
transcription activation of interferon A genes. J. Biol. Chem. 273, 29210–29217.
18. Barnes, B. J., Moore, P. A., and Pitha, P. M. (2001) Virus-specific activation of a
novel interferon regulatory factor, IRF-5, results in the induction of distinct inter-
feron alpha genes. J. Biol. Chem. 276, 23382–23390.
19. Barnes, B., Lubyova, B., and Pitha, P. M. (2002) On the role of IRF in host
defense. J. Interferon Cytokine Res. 22, 59–71.
20. Fitzgerald, K. A., McWhirter, S. M., Faia, K. L., Rowe, D. C., Latz, E., Golenbock,
D. T., et al. (2003) IKKepsilon and TBK1 are essential components of the IRF3
signaling pathway. Nat. Immunol. 4, 491–496.
21. Sharma, S., tenOever, B. R., Grandvaux, N., Zhou, G. P., Lin, R., and Hiscott, J.
(2003) Triggering the interferon antiviral response through an IKK-related path-
way. Science 300, 1148–1151.
22. McWhirter, S. M., Fitzgerald, K. A., Rosains, J., Rowe, D. C., Golenbock, D. T.,
and Maniatis, T. (2004) IFN-regulatory factor 3-dependent gene expression is
defective in Tbk1-deficient mouse embryonic fibroblasts. Proc. Natl. Acad. Sci.
USA 101, 233–238.
Interferon Research 33
23. Jhang, Y. T., Lowther, W., Kellum, M., et al. (1998) Primary activation of inter-
feron A and interferon B gene transcription by interferon regulatory factor 3. Proc.
Natl. Acad. Sci. 95, 9837–9842.
24. Schafer, S. L., Lin, R., Moore, P. A., Hiscott, J., and Pitha, P. M. (1998) Regula-
tion of type I interferon gene expression by interferon regulatory factor-3. J. Biol.
Chem. 273, 2714–2720.
25. Wathelet, M. G., Lin, C. H., Parekh, B. S., Ronco, L. V., Howley, P. M., and
Maniatis, T. (1998) Virus infection induces the assembly of coordinately activated
transcription factors on the IFN-beta enhancer in vivo. Mol. Cell 1, 507–518.
26. Yie, J., Senger, K., and Thanos, D. (1999) Mechanism by which the IFN-beta
enhanceosome activates transcription. Proc. Natl. Acad. Sci. USA 96, 13108–13113.
27. Ren, B., Chee, K. J., Kim, T. H., and Maniatis, T. (1999) PRDI-BF1/Blimp-1
repression is mediated by corepressors of the Groucho family of proteins. Genes
Dev. 13, 125–137.
28. Au, W. C. and Pitha, P. M. (2001) Recruitment of multiple interferon regulatory
factors and histone acetyltransferase to the transcriptionally active interferon a
promoters. J. Biol. Chem. 276, 41629–41637.
29. Yeow, W. S., Au, W. C., Juang, Y. T., Fields, C. D., Dent, C. L., Gewert, D. R., et
al. (2000) Reconstitution of virus-mediated expression of interferon alpha genes
in human fibroblast cells by ectopic interferon regulatory factor-7. J. Biol. Chem.
275, 6313–6320.
30. Lu, R., Au, W. C., Yeow, W. S., Hageman, N., and Pitha, P. M. (2000) Regulation
of the promoter activity of interferon regulatory factor-7 gene. Activation by
interferon and silencing by hypermethylation. J. Biol. Chem. 275, 31805–31812.
31. Marie, I., Durbin, J. E., and Levy, D. E. (1998) Diffential viral induction of dis-
tinct interferon-α genes by positive feedback through interferon regulatory factor
7. EMBO J 17, 6660–6668.
32. Taniguchi, T. and Takaoka, A. (2001) A weak signal for strong responses: inter-
feron-alpha/beta revisited. Nat. Rev. Mol. Cell Biol. 2, 378–386.
33. Izaguirre, A., Barnes, B. J., Amrute, S., Yeow, W. S., Megjugorac, N., Dai, J., et
al. (2003) Comparative analysis of IRF and IFN-alpha expression in human plas-
macytoid and monocyte-derived dendritic cells. J. Leukoc. Biol. 74, 1125–1138.
34. Fitzgerald, K. A., Rowe, D. C., Barnes, B. J., Caffrey, D. R., Visintin, A., Latz, E.,
et al. (2003) LPS-TLR4 signaling to IRF-3/7 and NF-kappaB involves the toll
adapters TRAM and TRIF. J. Exp. Med. 198, 1043–1055.
35. Mittrucker, H. W., Matsuyama, T., Grossman, A., Kundig, T. M., Potter, J.,
Shahinian, A., et al. (1997) Requirement for the transcription factor LSIRF/IRF4
for mature B and T lymphocyte function. Science 275, 540–543.
36. Schiavoni, G., Mattei, F., Sestili, P., Borghi, P., Venditti, M., Morse, H. C., 3rd, et
al. (2002) ICSBP is essential for the development of mouse type I interferon-
producing cells and for the generation and activation of CD8alpha(+) dendritic
cells. J. Exp. Med. 196, 1415–1425.
37. Tamura, T. and Ozato, K. (2002) ICSBP/IRF-8, its regulatory roles in the devel-
opment of myeloid cells. J. Interferon Cytokine Res. 22, 145–152.
34 Kunzi and Pitha
38. Barnes, B. J., Kellum, M. J., Pinder, K. E., Frisancho, J. A., and Pitha, P. M.
(2003) Interferon regulatory factor 5, a novel mediator of cell cycle arrest and cell
death. Cancer Res. 63, 6424–6431.
39. Takaoka, A., Hayakawa, S., Yanai, H., Stoiber, D., Negishi, H., Kikuchi, H., et al.
(2003) Integration of interferon-alpha/beta signalling to p53 responses in tumour
suppression and antiviral defence. Nature 424, 516–523.
40. Bach, E. A., Aguet, M., and Schreiber, R. D. (1997) The IFN gamma receptor: a
paradigm for cytokine receptor signaling. Annu. Rev. Immunol. 15, 563–591.
41. Brierley, M. M. and Fish, E. N. (2002) Review: IFN-alpha/beta receptor interac-
tions to biologic outcomes: understanding the circuitry. J. Interferon. Cytokine
Res. 22, 835–845.
42. Mogensen, K. E., Lewerenz, M., Reboul, J., Lutfalla, G., and Uze, G. (1999) The
type I interferon receptor: structure, function, and evolution of a family business.
J. Interferon Cytokine Res. 19, 1069–1098.
43. Darnell, J. E. J., Kerr, I. M., and Stark, G. R. (1994) Jak-STAT pathways and
transcriptional activation in response to IFNs and other extracellular signaling
proteins. [Review]. Science 264, 1415–1421.
44. Pestka, S., Langer, J. A., Zoon, K. C., and Samuel, C. E. (1987) Interferons and
their actions. Annu. Rev. Biochem. 56, 727–777.
45. Grieder, F. B. and Vogel, S. N. (1999) Role of interferon and interferon regulatory
factors in early protection against Venezuelan equine encephalitis virus infection.
Virology 257, 106–118.
46. Muller, U., Steinhoff, U., Reis, L. F., Hemmi, S., Pavlovic, J., Zinkernagel, R. M.,
et al. (1994) Functional role of type I and type II interferons in antiviral defense.
Science 264, 1918–1921.
47. Huang, S., Hendriks, W., Althage, A., Hemmi, S., Bluethmann, H., Kamijo, R., et
al. (1993) Immune response in mice that lack the interferon-gamma receptor. Sci-
ence 259, 1742–1745.
48. de Veer, M. J., Holko, M., Frevel, M., Walker, E., Der, S., Paranjape, J. M., et al.
(2001) Functional classification of interferon-stimulated genes identified using
microarrays. J Leukoc Biol, 69, 912–920.
49. Der, S. D., Zhou, A., Williams, B. R., and Silverman, R. H. (1998) Identification
of genes differentially regulated by interferon alpha, beta, or gamma using oligo-
nucleotide arrays. Proc. Natl. Acad. Sci. USA 95, 15623–15628, 1998.
50. Rebouillat, D., Hovnanian, A., David, G., Hovanessian, A. G., and Williams, B.
R. (2000) Characterization of the gene encoding the 100-kDa form of human 2',5'
oligoadenylate synthetase. Genomics 70, 232–240.
51. Samuel, C. E. (2001) Antiviral actions of interferons. Clin. Microbiol. Rev. 14,
778–809.
52. Williams, B. R. (1999) PKR; a sentinel kinase for cellular stress. Oncogene 18,
6112–6120.
53. Pitossi, F., Blank, A., Schroder, A., Schwarz, A., Hussi, P., Schwemmle, M., et al.
(1993) A functional GTP-binding motif is necessary for antiviral activity of Mx
proteins. J. Virol. 67, 6726–6732.
Interferon Research 35
54. Pavlovic, J., Arzet, H. A., Hefti, H. P., Frese, M., Rost, D., Ernst, B., et al. (1995)
Enhanced virus resistance of transgenic mice expressing the human MxA protein.
J. Virol. 69, 4506–4510.
55. Cattaneo, R. (1994) Biased (A{rarrow}I) hypermutation of animal RNA virus
genomes. Curr. Opin. Genet. Dev. 4, 895–900.
56. O’Hara, P. J., Nichol, S. T., Horodyski, F. M., and Holland, J. J. (1984) Vesicu-
lar stomatitis virus defective interfering particles can contain extensive genomic
sequence rearrangements and base substitutions. Cell 36, 915–924.
57. Haas, A. L., Ahrens, P., Bright, P. M., and Ankel, H. (1987) Interferon induces a
15-kilodalton protein exhibiting marked homology to ubiquitin. J. Biol. Chem.
262, 11315–11323.
58. Malakhova, O. A., Yan, M., Malakhov, M. P., Yuan, Y., Ritchie, K. J., Kim, K. I.,
et al. (2003) Protein ISGylation modulates the JAK-STAT signaling pathway.
Genes Dev. 17, 455–460.
59. Masci, P., Bukowski, R. M., Patten, P. A., Osborn, B. L., and Borden, E. C. (2003)
New and modified interferon alfas: preclinical and clinical data. Curr. Oncol. Rep.
5, 108–113.
60. Kawai, T., Sato, S., Ishii, K. J., Coban, C., Hemmi, H., Yamamoto, M., et al.
(2004) Interferon-α induction through Toll-like receptors involves a direct inter-
action of IRF7 with MyD88 and TRAF6. Nat. Immun. 5, 1061–1068.
61. Schoenemeyer, A., Barnes, B. J., Mancl, M. E., Latz, E., Goutagny, N., Pitha, P.
M., et al. (2005) The interferon regulatory factor, IRF5, is a central mediator of
TLR7 signaling. J. Biol. Chem. Jan 28 (in press).
62. Takaoka, A., Yanai, H., Kondo, S., Duncan, G., Negishi, H., Mizutani, T., et al.
(2005) Integral role of IRF-5 in the gene induction programme activated by Toll-
like receptors. Nature 434, 243–249.