A scientific team, from Northwestern University, has
just published new research in the prestigious medical journal
Virology that may ultimately prove to be the first animal
model for CFIDS/ME, a disease that affects millions of people
here in the U.S. The group's publication was formally titled
"Enabled interferon
signaling evasion in an immune-competent transgenic mouse
model of Parainfluenza Virus-5 infection."
Background:
In March of 2006, the National CFIDS Foundation (NCF)
contacted Robert Lamb, Ph.D., Sc.D., at Northwestern University,
to potentially assist the Foundation with its ongoing
research efforts that revolved around Parainfluenza Virus-5
(PIV-5) infection and its direct effect on STAT1, a key
protein responsible for host innate immunity. Dr. Lamb,
who is the John Evans Professor of Molecular and Cellular
Biology and Investigator at the Howard Hughes Medical
Institute, is one of this country's preeminent research
scientists in the field of virology. He is a past president
of the American Society for Virology, a member of the
National Academy of Sciences and a Fellow of the American
Academy of Arts and Sciences. In addition, he is a co-author
of Field's Virology, a book considered to be the 'bible'
for virologists. The NCF approached Dr. Lamb primarily
because his research laboratory investigates the molecular
structure and the mechanism of replication of PIV-5.
According to Dr. Lamb, parainfluenza viruses "cause
many biologically and economically important diseases
of humans and lower animals." As such, "most
viruses induce interferons, cytokines that defend the
cell from a virus infection. Thus, most viruses encode
proteins that defeat either induction of interferon synthesis
or prevent
the induction of transcription of cellular genes caused
by interferons binding to their receptors." In the
case of PIV-5, its "V protein mediates the proteasome-mediated
degradation of the transcription factor STAT1 (signal
transducer and activator of transcription). We are examining
the pathway by which the V protein mediates STAT1 destabilization."
To the NCF, Dr. Lamb's research was critically important
due to the fact that acquired STAT1 deficiencies had been
previously identified in CFIDS/ME patients by three research
groups
worldwide. These included Kenny DeMeirleir, M.D., Ph.D.,
who is Chief Scientist with R.E.D. Laboratories in Belgium
and co-editor of the Journal of Chronic Fatigue Syndrome
as well as a member of the Board of
Directors for the International Association for Chronic
Fatigue Syndrome (IACFS); Robert Suhadolnik, Ph.D., who
is Professor of Biochemistry at Temple University School
of Medicine in Philadelphia; and Donald Carrigan, Ph.D.
and Konstance Knox, Ph.D., who are founding scientists
of the Institute for Viral Pathogenesis in Milwaukee,
whose STAT1/PIV-5 research was directly funded by the
NCF and whose STAT1 research was formally presented at
an American Association for Chronic Fatigue Syndrome (AACFS)
conference in 2004.
Meetings between Dr. Lamb and another Northwestern University
scientist, Dr. Curt Horvath, had taken place shortly after
the NCF's research data had been thoroughly reviewed.
It was then determined that
a postdoc would be assigned as a liaison to the NCF and
to pursue some initial research studies that would be
completed by the Horvath Laboratory at Northwestern. The
postdoc assigned to the NCF's efforts
was Thomas Kraus, Ph.D. whose research for this work was
funded by a pilot grant from the Evanston Northwestern
Healthcare Medical Group.
Curt Horvath, Ph.D., has his own laboratory at Northwestern
that focuses on signal transduction and gene expression
in mammalian cells. The NCF had prior communications with
Dr. Horvath when he held a position at Mount Sinai School
of Medicine in New York. Since the formation of his new
lab, his research group now explores the specific biology
of STAT proteins. Because STAT proteins have a tight relationship
with
interferons, there is an important interplay between an
infection by a pathogen and the subsequent cellular defensive
response by the host's immune system. Simply stated, Dr.
Horvath's group explores how viruses evade the host interferon
(IFN) response. His group does this through the use of
parainfluenza viruses. More specifically, these scientists
utilize one member of the parainfluenza virus family,
PIV-5, to learn how this rubulavirus directly targets
and degrades STAT1 to evade the immune system of the host.
This is worth noting since preliminary research studies
by the NCF and others had identified PIV-5 infections
in CFIDS/ME patients.
Newest Research:
According to this latest paper, "The co-evolution
of viruses with their hosts has resulted in diverse mechanisms
to subvert the anti-viral immune system. Understanding
how these virulence factors affect viral pathogenesis
is a critical first step in identifying targets for pharmaceutical
intervention or vaccine development. The paramyxovirus
PIV-5 has been implicated in upper respiratory tract disease
and has been isolated from the cerebral spinal fluid of
a dog with posterior paralysis. In humans, PIV-5 has been
linked to both multiple sclerosis and chronic fatigue
and immune dysfunction syndrome, although direct causative
associations are poorly understood. PIV-5 can persistently
infect cells and has been isolated from several cultured
cell lines.
The observation that humans are one of the favored hosts
for PIV-5 replication is linked to the virus's efficacy
in blocking type I and type II interferon signaling as
a result of the specific degradation of the interferon
signaling molecule, STAT1. PIV-5 induced STAT1 degradation
requires the actions of a single viral protein known as
V."
The authors continue, "To validate these observations
in an intact animal, and as a means to establish a model
system to better understand how the ability to block IFN
signaling affects viral pathogenesis in
vivo, a transgenic mouse...was created. These mice are
normal by all criteria, but unlike WT (wild type) mice,
infection with PIV-5 induces loss of STAT1 and inhibition
of IFN signaling, recapitulating the phenotype observed
in cultured cells. Furthermore, results indicate that
the enabled IFN signaling inhibition is advantageous to
virus replication in vivo, as the lungs of PIV-5 infected
transgenic mice contain more virus than wild-type mice.
The increased viral load resulted in a coordinate increase
in the expression of inflammatory
signaling proteins....This confirms that the ability to
limit PIV-5 replication is impaired in the transgenic
mouse."
One of the conclusions that these authors reach is that
these results "support the conclusion that PIV-5
mediated STAT1 degradation in the lungs of the transgenic
mice can dampen the innate antiviral response and allow
for unrestricted viral replication....these experiments
show that viral IFN evasion of PIV-5 results in an immediate
increase in viral replication at the site of primary infection
followed by an increase in a local inflammatory response."
Discussion:
The authors state, "PIV-5 is a zoonotic virus found
in humans whose pathogenesisis uncertain. In immuno-competent
mice, PIV-5 appears to be non-pathogenic. However, because
its normal IFN evasion strategies are compromised, efficient
replication of the virusis restricted from mice....In
the...transgenic mice described here,
PIV-5 is better able to recapitulate the human infection
due to the enabled block in IFN signaling, a critical
parameter for viral pathogenesis."
Continuing their discussion, "In this unique animal
infection model, IFN signaling and antiviral responses
remain intact, providing the ability to examine virus
replication in a more natural context of a fully immune-competent
host. This situation differs greatly from strategies used
previously to investigate PIV-5 immune responses and pathogenesis.
In previous reports, immune compromised mice were used
to study the immune response to and pathogenesis of PIV-5
infections. When SCID (severe combined immune deficiency)
mice
were used, PIV-5 infection resulted in a short-term weight
loss and efficient recovery from infection, leading to
the conclusion that the adaptive immune system is not
vital to the antiviral immune response to PIV-5. Indeed
these studies were the first to demonstrate the importance
of IFN responses in controlling PIV-5 infection. Later
studies took advantage of mice harboring a deficiency
in the STAT1 gene. In this situation, the host is systemically
deficient in responses to both type I and type II IFN's,
causing dramatic consequences on innate and adaptive immunity.
Infection of STAT1 deficient mice with PIV-5 results in
100% mortality, dramatically different from the outcome
of any natural PIV-5 infection reported. These data prove
that the virus can
replicate efficiently in mice, and that the innate immune
response is critical. However, a drawback to these immune-compromised
mouse experiments is that it is not possible to determine
the natural progression of pathogenesis during infection
or evaluate the contributions of host responses to viral
pathogenesis. Based on our analysis...during a natural
PIV-5 infection, we expect that STAT1 would be degraded
in the infected cells, leaving the STAT1-dependent immune
response of non-infected cells intact."
Conclusion:
The authors comment that "Although PIV-5 does not
robustly infect murine (rat/mouse) cells for reasons that
may include differences in receptor binding and membrane
fusion as well as immune effects, low level persistent
infections can be established in cultured mouse cells....It
is quite interesting to note that in infected transgenic
mice, where IFN evasion has led to an early increase in
viral load, there is a parallel increase in inflammatory
response. Based on these findings, it is tempting to speculate
that PIV-5 mediated IFN evasion offers only a short-lived
advantage to the virus, and that clearance by the host
immune system occurs efficiently with or without IFN evasion.
In other words, the consequence of IFN evasion for PIV-5
is an increase in the viral load at the primary site of
infection, providing a short-term increase in viral load
that also may heighten the chance of
horizontal transmission. Further experimentation is required
to test this concept. PIV-5 has long served as a prototypic
member of the larger Paramyxovirus family. This family
of viruses includes re-emerging viruses like measles and
mumps, as well as newly emerging deadly viruses Hendra
and Nipah virus. All of these pathogenic
paramyxoviruses express V proteins which inhibit IFN responses.
In all cases, the consequence of IFN evasion has only
been examined in vitro. The...transgenic model described
here provides an excellent experimental
system to probe the consequences of innate immune evasion
during infection of an intact host organism. The data
reported here lay the foundation to study the role that
IFN evasion has on adaptive immune responses, viral pathogenesis,
disease progression, virus clearance and virus transmission."
Summary:
