Download Immune control of mammalian gamma- herpesviruses: lessons from

Journal of General Virology (2009), 90, 2317–2330
Review
DOI 10.1099/vir.0.013300-0
Immune control of mammalian gammaherpesviruses: lessons from murid herpesvirus-4
P. G. Stevenson,1 J. P. Simas2 and S. Efstathiou1
Correspondence
1
P. G. Stevenson
2
[email protected]
Division of Virology, Department of Pathology, University of Cambridge, UK
Instituto de Microbiologia e Instituto de Medicina Molecular, Faculdade de Medicina,
Universidade de Lisboa, Portugal
Many acute viral infections can be controlled by vaccination; however, vaccinating against
persistent infections remains problematic. Herpesviruses are a classic example. Here, we discuss
their immune control, particularly that of gamma-herpesviruses, relating the animal model provided
by murid herpesvirus-4 (MuHV-4) to human infections. The following points emerge: (i) CD8+
T-cell evasion by herpesviruses confers a prominent role in host defence on CD4+ T cells. CD4+
T cells inhibit MuHV-4 lytic gene expression via gamma-interferon (IFN-c). By reducing the lytic
secretion of immune evasion proteins, they may also help CD8+ T cells to control virus-driven
lymphoproliferation in mixed lytic/latent lesions. Similarly, CD4+ T cells specific for Epstein–Barr
virus lytic antigens could improve the impact of adoptively transferred, latent antigen-specific
CD8+ T cells. (ii) In general, viral immune evasion necessitates multiple host effectors for optimal
control. Thus, subunit vaccines, which tend to prime single effectors, have proved less successful
than attenuated virus mutants, which prime multiple effectors. Latency-deficient mutants could
make safe and effective gamma-herpesvirus vaccines. (iii) The antibody response to MuHV-4
infection helps to prevent disease but is suboptimal for neutralization. Vaccinating virus carriers
with virion fusion complex components improves their neutralization titres. Reducing the infectivity
of herpesvirus carriers in this way could be a useful adjunct to vaccinating naive individuals with
attenuated mutants.
Herpesviruses present complicated and difficult
immune targets
Parasitism is ubiquitous and the immune systems of
multicellular organisms work mainly to reduce their
parasite loads. Vaccination can improve immune protection further by pre-empting natural infection; a major aim
of immunology is to deliver safe and effective vaccines.
Epidemic viruses rely on rapid lytic replication to transmit
before host immunity becomes effective. Blunting their
lytic replication can therefore protect both individuals and
populations. Neutralizing antibodies provide the best
defence (Zinkernagel & Hengartner, 2006). Since these
generally act by blocking receptor binding (Skehel & Wiley,
2000), a vaccine that reproduces viral receptor binding
epitopes generally elicits good protection. We have much
less idea how to protect against viruses that persist: because
they use immune evasion to extend host colonization and
transmission far beyond the narrow window that precedes
adaptive immunity, blunting lytic replication confers only
limited protection.
The herpesviridae account for many persistent mammalian
infections. Gamma-herpesviruses persist mainly in lymphocytes, beta-herpesviruses in monocytes and alphaherpesviruses in neurons. These different reservoirs have
013300 G 2009 SGM
some bearing on immune recognition; for example,
gamma-herpesvirus persistence requires intermittent viral
protein synthesis (Moorman et al., 2003; Fowler et al.,
2003). Nevertheless, the immune control of different
herpesviruses reveals many common themes. Human
experiments are difficult to perform and rarely reveal
mechanisms, so much of our knowledge of immune
control has come from other species, predominantly mice.
Unfortunately, viral immune evasion critically affects the
host–parasite balance and tends to be host-restricted,
making murine infections with human herpesviruses
problematic. Equivalent pathogens that behave more
normally in mice provide a useful alternative. These cannot
be used to test specific reagents but, by revealing basic
principles, they allow us to plan better clinical trials.
Alpha-herpesvirus study has the longest history, as herpes
simplex virus (HSV) is readily isolated from patients,
propagates well in vitro and can infect mice. The mouse
model played a major role in the development of antiviral
chemotherapy (Klein, 1982). However, it has limitations,
notably in immunological analysis; viral immune evasion is
an integral part of host colonization (Yewdell & Hill, 2002)
and many HSV immune evasion mechanisms simply do
not work in mice. Without an equivalent murid alpha-
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P. G. Stevenson, J. P. Simas and S. Efstathiou
herpesvirus for more realistic in vivo analysis, this has
created something of an impasse. The functional analysis of
immunity to beta-herpesviruses has centred on murine
cytomegalovirus (MCMV) (Hengel et al., 1998; Reddehase
et al., 2008) in which an extremely complex equilibrium is
established that depends on multiple host defences and
multiple viral evasions. Quantifying the contributions of
individual host and viral genes to this equilibrium
continues to provide a major challenge. The gammaherpesviruses were, for many years, the least understood
mammalian herpesviruses. Although Epstein–Barr virus
(EBV) was discovered almost 50 years ago (Epstein et al.,
1964), its narrow species tropism has severely constrained
functional analysis. This all changed with the discovery of
murid herpesvirus-4 (MuHV-4; archetypal strain MHV68) (Blaskovic et al., 1980); its relative simplicity
(compared with MCMV) and its capacity to establish a
realistic infection in inbred mice have enabled rapid
progress, and our knowledge of gamma-herpesvirus
pathogenesis is now at least as complete as for the alphaand beta-herpesviruses. This review therefore concentrates
on the gamma-herpesviruses and MuHV-4.
increased proportion of CD4+ T cells in EBV adoptive
transfers seems to correlate with a better therapeutic effect
(Haque et al., 2007), and the only attempt at priming CD8+
T cells to date, although weak, failed to reduce the rate of
EBV seroconversion (Elliott et al., 2008).
Gamma-herpesviruses: does CD8+ T-cellmediated control explain the pathogenesis of
human infections?
An early finding with MuHV-4 was that high dose lung
infection is acutely lethal to CD8+ T-cell-depleted BALB/c
mice (Ehtisham et al., 1993). A chronic wasting disease in
CD4+ T-cell-deficient C57BL/6 mice was consequently
interpreted as CD8+ T-cell exhaustion without the help of
CD4+ T cells (Cardin et al., 1996). However, CD8+ T cells
were found to be fully functional in the ill mice (Stevenson et
al., 1998; Belz et al., 2003) and boosting them to high levels
did not affect survival much (Belz et al., 2000). Also, MuHV4-infected, CD8+ T-cell-deficient C57BL/6 mice remained
healthy, as did CD8+ T-cell-deficient BALB/c mice given a
low dose infection, whereas mice lacking both CD4+ and
CD8+ T cells always succumbed (Stevenson et al., 1999a).
Therefore, CD8+ T cells help to limit MuHV-4 lytic
replication, but are generally neither necessary nor sufficient
to prevent lytic-based pathologies. Instead, there is an
important role for CD4+ T cells as either direct effector cells
or helpers of the antibody response (Table 1).
Two human gamma-herpesviruses are known, EBV and the
Kaposi’s sarcoma-associated herpesvirus (KSHV), both of
which can cause disease. However, EBV is both more
prevalent and more frequently pathogenic. It has also been
studied much more intensively than KSHV. Thus, the
broad picture of EBV is well-defined – transmission via
saliva, an acute, self-limiting, lymphoproliferative illness
and persistence in circulating memory B cells – while that
of KSHV, while probably similar, is not. Of the human
gamma-herpesviruses, therefore, we consider mainly EBV.
Latent EBV can cause tumours in vivo and transforms
primary B cells in vitro. Immunological analysis has
consequently focussed on the recognition of viral latency
gene products expressed in transformed B cells, mainly by
CD8+ T cells (Rickinson & Moss, 1997). B-cell differentiation
seems to terminate the proliferation of many EBV-infected B
cells in vivo (Babcock et al., 1999; Hadinoto et al., 2008), but
the pathological consequences of T-cell deficiency imply that
immune mechanisms are also important. An important
unknown is how far in vivo immune control matches the
CD8+ T-cell-mediated killing that is defined in vitro.
Adoptively transferred, EBV-stimulated T cell populations,
which are for the most part CD8+, can suppress some forms
of EBV-induced lymphoproliferative disease (Gottschalk et
al., 2005), which supports the idea that CD8+ T cells are
important. However, the direct evidence for CD8+ T-cellmediated control is limited: as with alpha- and betaherpesviruses, CD4+ T-cell deficiencies lead to disease
(Carneiro-Sampaio & Coutinho, 2007) while CD8+ T-cell
deficiencies do not (Cerundolo & de la Salle, 2006); an
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The contribution of CD8+ T cells to MuHV-4
control is limited
MuHV-4 provided the first opportunity to test directly the
role of CD8+ T cells in gamma-herpesvirus pathogenesis.
MuHV-4 is genetically closer to KSHV than to EBV (Virgin
et al., 1997), but is B-cell tropic like EBV and shows a
similar approach to host colonization (Nash et al., 2001);
for example, both MuHV-4 (Bowden et al., 1997) and EBV
(Roughan and Thorley-Lawson, 2009) exploit host germinal centres for B-cell colonization. Although MuHV-4
naturally infects Apodemus flavicollis mice (Kozuch et al.,
1993), it also behaves much like a natural parasite in Mus
musculus-derived laboratory strains, persisting without
disease unless there is immune suppression (Virgin &
Speck, 1999). Crucially, its immune evasion genes still seem
to work (Stevenson & Efstathiou, 2005).
MuHV-4-infected b2-microglobulin-deficient BALB/c mice,
which largely lack classical CD8+ T cells, do show a
threefold increase in lymphoproliferative disease compared
with uninfected controls (Tarakanova et al., 2005).
However, such disease does not occur in b2-microglobulin-deficient C57BL/6 mice; b2-microglobulin-deficient
mice have several other deficits, including a lack of natural
killer (NK) T cells, low serum IgG and altered NK cell
repertoires, and the tumours observed largely lacked viral
genomes. Therefore, whether CD8+ T cells are required to
limit MuHV-4-driven lymphoproliferation remains unclear.
Latent antigen recognition by CD8+ T cells
After intranasal MuHV-4 infection of immunocompetent
mice, the extent of lymphoid infection depends mainly on
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Journal of General Virology 90
Gamma-herpesvirus immunity – a review
Table 1. Key lessons on MuHV-4 immune control from
knockout mice
Mouse
Immunodeficiency
2/2
b2M
C57BL/6
b2M2/2 BALB/c
b2/2
I-A
C57BL/6
mMT C57BL/6
IFN-c2/2 C57BL/6
IFN-cR2/2 BALB/c
+
CD8 T cellsD
CD8+ T cells
CD4+ T cells
B cells
IFN-c
IFN-c receptor
Virus load Disease*
Increased
Increased
Increasedd
Increased§
Normal
Increased||
No
Yes
Yes
No
No
Yes
*The disease of b2M2/2 BALB/c mice is mainly lymphoproliferative;
that of I-Ab2/2 and IFN-cR2/2 mice reflects chronic lytic replication.
Db2M2/2 mice also have no CD1-restricted NKT cells, reduced serum
IgG concentrations and altered NK cell repertoires.
dDespite an acute latency amplification deficit, chronic lytic
replication is increased.
§Normal B cell latency is abolished but virus loads are increased in
myeloid cells.
||Mainly greater chronic lytic replication.
latency-associated lymphoproliferation (Stevenson et al.,
1999c). However, in immunodeficient mice, lytic and
latent control are readily confused. Thus, MuHV-4 latent
loads increase when CD8+ T cells are lacking (Stevenson
et al., 1999a; Tibbetts et al., 2002), but lytic replication also
increases and could seed more latency as a secondary event.
This occurs particularly with intraperitoneal infections,
because infectious virus seeds directly to the spleen.
A clearer picture of the function of latent antigen-specific
CD8+ T cells has come from analysing a defined MuHV-4
latent antigen, an H2Kd-restricted epitope in M2 (Husain
et al., 1999). M2 interferes with B cell receptor signal
transduction (Rodrigues et al., 2006) and is therefore
functionally equivalent to the EBV LMP-2A (Burkhardt
et al., 1992) and the KSHV K1 (Lee et al., 1998) proteins.
Mouse strains not recognizing M2, such as C57BL/6 (H2b),
have higher long-term latent loads than strains that do,
such as BALB/c (H2d); mutating the M2 epitope anchor
residues increases H2d mouse latent loads and restoring
epitope expression returns them to normal (Marques et al.,
2008). Therefore, latent antigen-specific CD8+ T cells help
to regulate long-term latent loads. Interestingly, H2b mice
show a massive expansion of non-classical Vb4+CD8+ T
cells (Braaten et al., 2006). This could be considered a
back-up defence when classical CD8+ T cell recognition
fails; the higher latent loads of H2b mice imply that the
control Vb4+CD8+ T cells exert is relatively weak.
Herpesvirus immune evasion limits CD8+ T cell
function
Although M2-specific CD8+ T cells clearly exert some
control over MuHV-4, it is difficult to estimate whether
their effect is proportionate to their numbers, that is
whether CD8+ T cell recognition is efficient. This is an
important concept for vaccination: if CD8+ T cells are
poorly efficient, then boosting their numbers is likely to
give only limited returns. An obvious consideration is viral
evasion (Stevenson, 2004).
Herpesvirus genes that inhibit major histocompatibility
complex (MHC) class I-restricted antigen presentation are
typically expressed early in lytic infection, presumably to
allow reactivation and transmission in the face of
established CD8+ T-cell immunity. The MuHV-4 K3
degrades MHC class I heavy chains (Boname & Stevenson,
2001; Lybarger et al., 2003) and the TAP peptide
transporter (Boname et al., 2004a). KSHV has two
homologues, K3 and K5, that degrade MHC class I heavy
chains and other substrates (Früh et al., 2002), and the EBV
BNLF2a inhibits TAP (Hislop et al., 2007) (Table 2).
Surprisingly, K32 MuHV-4 (Stevenson et al., 2002)
showed an additional, CD8-dependent defect in latencyassociated lymphoproliferation. This implied that K3
normally alleviates the acute, CD8+ T-cell-mediated
control of viral latency, and would explain the limited
impact of M2-based vaccination (Usherwood et al., 2001).
K3 mRNA is detectable in latently infected germinal centre
B cells, and K3 could therefore protect B cells directly
against CD8+ T cell attack. However, like most transacting herpesvirus evasion genes, K3 is predominantly a
lytic transcript (Coleman et al., 2003a); prominent early
lytic gene expression in sites of MuHV-4 latency (Milho
et al., 2009) suggests extensive interplay between lytic and
latent infections to which K3 could contribute. In support
of such an idea, MuHV-4 lacking its M11 apoptosis
inhibitor has a latency defect (de Lima et al., 2005), even
though M11 expression is minimal in B cells (Marques
et al., 2003). One way K3 might act is by downregulating
Table 2. MuHV-4 CD8+ T cell evasion mechanisms
Gene
K3
M3
ORF73
M2
Site of action
Mechanism
Human gamma-herpesvirus equivalents
Lytic+latent infections
Lytic+latent infections
Latency
Latency
MHC class I+TAP degradation
Chemokine binding
Poor antigen presentation
Selection of virus variants
KSHV K3, K5 and EBV BNLF2a
Possibly KSHV vMIPs and EBV vIL-10*
KSHV ORF73 and EBV EBNA-1
KSHV K1 and possibly EBV EBNA-3C
*These are functionally different from M3 but conform to the same scheme of a secreted lytic cycle protein that can provide immune evasion in
trans in a mixed lytic/latent lesion.
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P. G. Stevenson, J. P. Simas and S. Efstathiou
MHC class I-restricted antigen presentation in lytically
infected myeloid cells (Smith et al., 2007). These probably
carry virus to lymphoid tissue and, once there, express
early lytic evasion genes such as M3 (Marques et al., 2003),
which binds chemokines (Parry et al., 2000; van Berkel
et al., 2000) and inhibits CD8+ T cell function (Bridgeman
et al., 2001; Rice et al., 2002). Therefore, lytic K3 expression
could both increase virus seeding to B cells and help to
protect B cells via M3. EBV and KSHV lack M3, but encode
other secreted evasion proteins (Nicholas, 2005) and are
unlikely to be any less complex than MuHV-4.
Cis-acting evasion protects gamma-herpesvirus
episome maintenance
Viral evasion increases the extent of acute, virus-driven
lymphoproliferation and probably allows it to continue
long-term at a low level. Nevertheless, by 2–3 months after
infection with EBV or MuHV-4, lymphoproliferation is
largely controlled. The prevalent latent state is then
quiescence without viral protein expression (ThorleyLawson, 2001). While this is presumably inaccessible to
immune attack, when latently infected cells divide, their viral
episomes must be replicated and segregated by a viral
episome maintenance protein. Gamma-herpesviruses have
consequently evolved mechanisms to keep episome maintenance immunologically silent. The EBV episome maintenance protein, EBNA-1, limits its epitope presentation to
CD8+ T cells through transcriptional (Sample et al., 1992)
and translational (Levitskaya et al., 1995; Yin et al., 2003)
auto-regulation. The MuHV-4 ORF73 episome maintenance protein is similar. If its cis-acting evasion is bypassed,
CD8+ T cells ablate latency (Bennett et al., 2005), indicating
that episome maintenance is normally protected.
CD4+ (Nikiforow et al., 2003) and CD8+ (Voo et al.,
2004) T cells can recognize EBNA-1 epitopes on in vitrotransformed B cells. However, such recognition is dosedependent (Mautner et al., 2004). EBNA-1 expression is
linked to the cell cycle (Davenport & Pagano, 1999) and in
vitro cell proliferation rates tend to be very high. Thus, in
vitro cultures or EBNA-1 expressed from heterologous
promoters (Fu et al., 2004) do not necessarily yield
physiologically relevant results. Tumours with high proliferation rates might present EBNA-1 in vivo, but such
tumours are unlikely to grow out in the first place because
EBV carriers generally have EBNA-1-specific T cells (Blake
et al., 2000). For MuHV-4, even the optimized expression
of a CD4+ T cell epitope in latency made no difference to
host colonization (Smith et al., 2006). It therefore seems
unlikely that T cells control gamma-herpesvirus latency
through the recognition of episome maintenance.
Direct CD4+ T cell effector function in MuHV-4
infection
Given the limits imposed by viral evasion, how might
CD4+ T cells contribute to host defence? One possibility is
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CD8+ T cell help, as described for lymphocytic choriomeningitis virus (LCMV) infection (Battegay et al., 1994).
However, herpesviruses and LCMV are ecologically quite
different: herpesviruses evade CD8+ T cell recognition,
whereas LCMV persists by inducing a partially tolerant
carrier state, like hepatitis B virus. MuHV-4-specific CD8+
T-cell responses seem not to require CD4+ T cell help
(Belz et al., 2003). Even for LCMV, CD4+ T cells may be
needed more for antibody to reduce viral loads than for
direct CD8+ T cell help (Thomsen et al., 1996). Thus,
while CD8+ T-cell responses can be CD4-dependent, this
seems not to apply in herpesvirus infections.
Other possibilities are B cell help and direct CD4+ T cell
effector function. The latter was addressed in MuHV-4 by
depleting T cell subsets from B-cell-deficient mice
(Christensen et al., 1999). CD4+ T cells were found to
be at least as important as CD8+ for controlling acute lytic
replication in this setting. Therefore, CD4+ T cells can be
directly antiviral, independent of CD8+ T cells or B cells.
This contrasts with influenza virus infection, in which
CD4+ T cells act almost entirely through B cell help
(Topham & Doherty, 1998).
Depleting CD8+ T cells plus gamma-interferon (IFN-c)
additively increased viral titres, whereas depleting CD4+ T
cells plus IFN-c did not. Therefore, CD4+ but not CD8+ T
cells act via IFN-c. CD4+ T cell antiviral effector function
was later confirmed to be CD8-independent and IFN-cdependent (Sparks-Thissen et al., 2005), and IFN-c was
found to suppress viral lytic gene expression directly in
myeloid cells (Steed et al., 2007). The importance of IFN-c
in protecting B-cell-deficient mice is consistent with
MuHV-4 causing disease in IFN-c-receptor-deficient mice
(Weck et al., 1997; Dutia et al., 1997). Why MuHV-4
should remain sensitive to IFN-c rather than evolving an
evasion mechanism is unclear. Its long-term transmission
may benefit from viral replication being suppressed when
there is significant inflammation, so as not to deplete the
latent pool non-productively or cause excessive harm to
the host. Whatever the evolutionary explanation, the end
result, as with MCMV (Polić et al., 1996), is that IFN-cproducing CD4+ T cells contribute significantly to viral
control.
CD4+ T cells and the control of MuHV-4 latency
The survival of MuHV-4-infected, CD8+ T cell-deficient
mice (Stevenson et al., 1999a) suggests that CD4+ T cells
might also help to limit virus-driven lymphoproliferation.
However, such a function has been hard to define as
MuHV-4 exploits CD4+ T cells to drive its lymphoproliferation in the first place (Usherwood et al., 1996). IFN-c
receptor-deficient mice show impaired control of latency
(Dutia et al., 1997), but IFN-c-deficient mice do not
(Sarawar et al., 1997) (the difference could reflect the
different genetic backgrounds of these knockouts or
additional complexity in the interaction between MuHV4 and IFN-c). Probably the main arguments for CD4+ T
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Gamma-herpesvirus immunity – a review
cells being important in the control of latency are that
priming mice with MuHV-4 mutants (Tibbetts et al., 2003;
Boname et al., 2004b; Fowler & Efstathiou, 2004), which
primes both CD4+ and CD8+ T-cells (Boname et al.,
2004b), reduces wild-type latency much more effectively
than priming just CD8+ T cells (Stevenson et al., 1999c;
Usherwood et al., 2001), and that CD4+ T cells are an
important component of the protection induced by
priming with MuHV-4 (McClellan et al., 2004).
Although CD4+ T cells seem to control MuHV-4 via IFNc, what they recognize is unclear. Most cells supporting
MuHV-4 lytic replication lack MHC class II expression.
Therefore, CD4+ T cells probably control lytic replication
indirectly, with antigen presentation by MHC class II+
cells inducing IFN-c that then protects other cell types
(that the presenting cells need not be infected reduces the
scope for viral evasion). CD4+ T cells are also unlikely to
combat latency directly, as the deliberate latent expression
of a CD4+ T cell target failed to reduce viral loads (Smith
et al., 2006). However, the low-level, non-cytopathic
expression of viral latent antigens also makes bystander
protection unlikely. Therefore, the effects of CD4+ T cells
on latency may reflect lytic antigen recognition. This would
be consistent with latency-deficient mutants inducing good
protection against wild-type latency (Boname et al., 2004b;
Fowler & Efstathiou, 2004).
When MuHV-4 is given intraperitoneally or when normal
antibody production is lacking, CD4+ T cells can reduce
the seeding of latency by reducing the extent of viral lytic
replication (Sparks-Thissen et al., 2004). However, after
intranasal infection of immunocompetent mice, blocking
lytic replication is insufficient to control latency (Stevenson
et al., 1999c), so another explanation of how lytic antigenspecific CD4+ T cells might normally act is required. One
possibility is that CD4+ T-cell-derived IFN-c blocks the
expression of viral early lytic genes in myeloid cells (Steed
et al., 2007). By reducing the secretion of evasion gene
products such as M3, this could expose latently infected B
cells to CD8+ T cell attack (Stevenson, 2004). Thus, CD4+
and CD8+ T cells would work together, but in a way
dictated by viral evasion rather than by pure immunology.
A need for both T cell subsets to achieve optimal control is
consistent with several points: MuHV-4 causes disease in
CD4+ T-cell-deficient mice (Cardin et al., 1996), MuHV-4
titres remain elevated in CD8-deficient C57BL/6 mice
(Stevenson et al., 1999a), MuHV-4 causes tumours in b2microglobulin-deficient BALB/c mice (Tarakanova et al.,
2005) and CD8+ or CD4+ T-cell priming alone is poorly
protective (Stewart et al., 1999; Liu et al., 1999).
Relating MuHV-4 immune control to EBV and
KSHV
The MuHV-4 M2 recognition data imply that CD8+ T
cells exert some control over long-term gamma-herpesvirus latent loads, but that their effectiveness is limited by
genetics: a host of a given MHC class I haplotype can only
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recognize viruses with presentable epitopes. Both M2
(Marques et al., 2008) and the KSHV K1 (Stebbing et al.,
2003) show evidence of strong positive selection for amino
acid diversity, presumably because less well-recognized
viruses achieve higher latent loads and therefore transmit
better to new hosts. Thus, a combination of human
leukocyte antigen (HLA) typing and viral latent gene
sequencing may be sufficient to predict EBV and KSHV
latent loads. Certainly, ignoring virus–HLA interactions
could miss an important source of individual variation.
Even with a small pool of latently expressed viral proteins,
some CD8+ T-cell recognition is likely in outbred humans
because the large number of MHC class I molecules
available (typically five or six rather than two or three in
genetically homozygous mice) increases the chance of
finding a presentable epitope. Therefore, it makes sense to
restore latent antigen-specific CD8+ T cells to immunodeficient patients. However, the impact of these cells will be
limited acutely by viral evasion and in the longer term by
HLA class I haplotype. Therefore, priming or boosting
latent antigen-specific CD8+ T cells in immunocompetent
patients seems less likely to be worthwhile.
Adoptively transferred T-cell populations are typically
biased towards CD8+ T cells because their numbers are
expanded with in vitro-transformed B cells that present
mainly HLA class I-restricted epitopes. If EBV lytic cycle
evasion proteins promote in vivo latency amplification, as
with MuHV-4 (Bridgeman et al., 2001), then increasing the
representation of EBV lytic antigen-specific CD4+ T cells
(Adhikary et al., 2006) in adoptive transfers might well
improve their effectiveness.
Antibody in host defence against gammaherpesviruses
Although CD4+ T cells can be antiviral through IFN-c
production, they might also protect immunocompetent
hosts by promoting antibody responses. Antibody certainly
helps to contain persistent MuHV-4 (Gangappa et al.,
2002; Kim et al., 2002). However, MuHV-4 tends to cause
disease in antibody-deficient mice by chronic lytic
replication and is, therefore, different from EBV in this
regard. A role for antibody in host defence against EBV has
been hard to define because B-cell-deficient patients,
lacking the main viral latency reservoir, do not support
normal persistence (Faulkner et al., 2000).
The failure of acyclovir to reduce latent loads during
infectious mononucleosis (Yao et al., 1989a) or in EBV
carriers (Yao et al., 1989b) suggests that established EBV
latency is impervious to antibody, as viral lytic replication
is presumably the only viable antibody target. However, the
acyclovir experiment (Yao et al., 1989b) lasted only 2 weeks
– the half-life of EBV-infected B cells even in acute
infection is approximately 1 week (Hadinoto et al., 2008) –
so latent load reductions may have been hard to detect.
Also, acyclovir was given relatively late in infection:
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P. G. Stevenson, J. P. Simas and S. Efstathiou
infectious mononucleosis only occurs once EBV latency is
well established (Hoagland, 1964). Passive antibody can
reduce acute lytic replication by MuHV-4 (D.E. Wright &
P.G. Stevenson, unpublished data). Therefore, the use of
passive antibody to protect immunocompromised patients
exposed to primary EBV should probably be explored
further. The protection against acute MuHV-4 by antibody
is largely IgG Fc receptor-dependent and is therefore likely
to involve antibody-dependent cytotoxicity (D.E. Wright &
P.G. Stevenson, unpublished data), consistent with similar
findings for HSV (Hayashida et al., 1982).
Gamma-herpesvirus neutralization
Virion neutralization by pre-formed antibody has the
potential to block herpesvirus infection completely.
However, in vivo neutralization is not well understood
for any herpesvirus, because host entry remains ill-defined
(Table 3). It has been hypothesized that incoming EBV
virions directly infect B cells in tonsillar crypts (Faulkner
et al., 2000). However, direct evidence for this is lacking. B
cell infection by cell-free virions is blocked by anti-gp350
antibodies (Thorley-Lawson & Geilinger, 1980). Therefore,
the failure of gp350 vaccination to reduce the rate of EBV
seroconversion (Sokal et al., 2007) argues that B cell
infection by cell-free virions may not be essential for in vivo
host colonization. Incoming virions could instead infect
epithelial cells without engaging gp350 (Janz et al., 2000)
and then reach B cells through antibody-secluded cell–cell
contacts.
The possibility that incoming MuHV-4 virions might reach
B cells directly was addressed with replication-deficient
mutants. Viral DNA persisted in the spleen after intraperitoneal inoculation (Tibbetts et al., 2006; Kayhan et al.,
2007) but did not reach the spleen after intranasal
inoculation under anaesthesia (Moser et al., 2006;
Kayhan et al., 2007) and persisted in lung B cells in one
study (Moser et al., 2006) but not in another (Kayhan et
al., 2007). The conservative conclusion would be that
circulating B cells are not directly accessible to incoming
virions. In vivo infection provides a crucial test of any
neutralization because it presents both more barriers than
in vitro infections, for example mucinous secretions, and
more opportunities, for example a multiplicity of cell types.
However, it is clearly important to use a realistic
inoculation. Intraperitoneal injection bypasses important
features of natural infection and even intranasal infections
are unsatisfactory if general anaesthesia and large inoculation volumes are used to deliver virions directly to the
lung. When mice spontaneously inhale a small volume of
MuHV-4 inoculum without anaesthesia, acute lytic
replication occurs only in the nose, not in the lung
(Milho et al., 2009). Systemic persistence is nevertheless
robustly established. In contrast, oral virus is very poorly
infectious (Milho et al., 2009). Therefore, natural transmission is likely to involve only the upper respiratory tract.
In contrast with lower respiratory tract infection (Coleman
et al., 2003b), thymidine kinase-deficient MuHV-4 fails to
establish a significant infection via the upper respiratory
tract (Gill et al., 2009). Virions entering by this route may
therefore have not only to replicate lytically but also to do
so in terminally differentiated cells before reaching B cells.
This is an important consideration for antiviral therapy as
well as for neutralization: acyclovir could potentially
have some effect against EBV if given very early after
exposure.
A striking finding with MuHV-4 – although so far only
applied to lung infection – has been that immune sera
neutralize virions much less well for host entry than for
infection in vitro (Gillet et al., 2007a). Thus, it seems that in
vitro assays greatly overestimate neutralization, presumably
because they rely largely on blocks to cell binding (Gill
et al., 2006; Gillet et al., 2009a) that can be bypassed in vivo.
Notably, MuHV-4 virions exposed to immune sera bind
poorly to fibroblasts, but show enhanced infectivity for IgG
Fc receptor+ cells (Rosa et al., 2007).
Table 3. Gamma-herpesvirus neutralization
Glycoprotein target
gB
gH/gL (+gp42) (fusion)D
gH/gL (+gp70) (binding)d
gp350/gp150§
EBV neutralization
MuHV-4 neutralization
In vitro*
In vivo
In vitro
In vivo
Yes
Yes
No
Yes
Unknown
Unknown
Unknown
Unknown
Yes
Yes
Yes
No
Yes
Yes
No
No
*B cell infection. The neutralization of epithelial infection remains largely unexplored.
DEBV uses gH/gL/gp42 to fuse with B cells. MuHV-4 has no known equivalent to gp42.
dHere we distinguish gH/gL antibodies that block membrane fusion from those that block cell binding: for MuHV-4 to heparan sulfate and for EBV
to an unknown epithelial ligand. The MuHV-4 gp70 also binds to heparan sulfate, so a combined binding block must target both gH/gL and gp70.
EBV has no gp70 homologue.
§The EBV major variable glycoprotein, gp350, binds to CR2 on B cells. The MuHV-4 equivalent, gp150, does not bind to B cells and functions
mainly in virion release.
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Gamma-herpesvirus immunity – a review
In contrast with cell binding blocks, fusion blocks should
be universal and antibodies to gH/gL or gB – the
conserved, essential components of herpesvirus fusion
(Turner et al., 1998) – can act post-binding (Gill et al.
2006; Gillet et al., 2006) to inhibit both IgG Fcindependent and IgG Fc-dependent MuHV-4 infections
(Gillet et al., 2007a). However, post-binding neutralization
is far from straightforward. An association between gH/gL
and gB (Gillet & Stevenson, 2007a) provides mutual
shielding (Gillet & Stevenson, 2007b; Gillet et al., 2009b)
until post-endocytic low pH triggers gL dissociation and
gB/gH conformation changes (Gillet et al., 2008a, b).
Neutralization is consequently forced to act by gH/gL
stabilization or steric hindrance, neither of which is easy to
achieve. This may nevertheless be the best chance of
blocking host entry.
The major gamma-herpes virion glycoprotein as a
neutralization target
All gamma-herpesviruses share a positionally conserved
but sequence-variable major glycoprotein: gp350 in EBV,
K8.1 in KSHV and gp150 in MuHV-4. None is required for
fusion, arguing that they are unlikely to be good
neutralization targets. Unlike gp350, the MuHV-4 gp150
does not bind to B cells. Instead it regulates epithelial
infection by making cell binding heparan sulfate-dependent (de Lima et al., 2004). Interestingly, the EBV gp350 also
negatively regulates epithelial cell binding (Shannon-Lowe
et al., 2006), suggesting that these proteins share a common
function of epithelial virion release.
Gp150 also helps MuHV-4 evade neutralization, an
important function for released virions. Antibodies to
gp150 do not neutralize. Instead they are responsible for
immune sera enhancing infection via IgG Fc receptors
(Gillet et al., 2007b). Gp150 is the immunodominant
MuHV-4 antibody target (Gillet et al., 2007b), so MuHV-4
virions that are blocked for normal cell binding by immune
sera can remain infectious via a gp150–antibody–IgG Fc
receptor link (Rosa et al., 2007). The most immunogenic
region of gp150 is shared by gp350 and the KSHV K8.1,
suggesting that this evasion mechanism is conserved. Thus,
gB and gH/gL may be better in vivo EBV neutralization
targets than gp350.
All mammalian herpesviruses probably conform
to similar pathogenetic schemes
The phenotypes of genetic and acquired human immunodeficiencies (Carneiro-Sampaio & Coutinho, 2007) suggest
that the key elements of alpha-, beta- and gammaherpesvirus host defence are broadly similar. There is also
remarkable immunological consistency between MCMV
(Polić et al., 1998) and MuHV-4, the best explored
experimental herpesvirus infections. For each, multiple
effector mechanisms contribute to control, and CD4+ T
cells are at least as important as CD8+. The main
http://vir.sgmjournals.org
difference between MCMV and MuHV-4 is that NK cells
contribute less to controlling MuHV-4 (Usherwood et al.,
2005). This presumably reflects that more comprehensive
T-cell evasion by MCMV forces more reliance on NK
function. It might be speculated that MCMV and MuHV-4
are following different evolutionary strategies: immune
evasion genes tend to be species-specific, so MCMV, with
many such genes, is being as successful as possible in one
host while losing the flexibility to switch to others; MuHV4 has fewer evasion genes but appears able to infect more
species (Kozuch et al., 1993); a close relative of MuHV-4
(Andrew Davison, personal communication) has even been
isolated from a shrew (Chastel et al., 1994). Few hosts
comparable to humans have survived, so the evolutionary
pressures on human herpesviruses may be subtly different.
However, the problems alpha- and beta-herpesviruses
cause when NK cell function is defective (CarneiroSampaio & Coutinho, 2007) argue that immune evasion
limits viral control by T cells.
How does poor CD8+ T-cell efficacy fit with the sizeable
CD8+ T-cell responses that herpesviruses often elicit? A
key point is whether these responses target cells central to
host colonization or only their derivatives. For example, do
the large populations of EBV lytic antigen-specific CD8+ T
cells found in infectious mononucleosis (Callan et al.,
1996) recognize the source of the problem (latency
amplification) or merely chase its tail (lytic reactivation)?
The latter could help to limit disease, but is unlikely to
achieve infection control. MuHV-4 elicits large lytic
antigen-specific CD8+ T-cell responses (Stevenson et al.,
1999b) that clearly do not control latency amplification,
since priming them fails to prevent it (Stevenson et al.,
1999c). Indeed, the expansion of these cells reflects a failure
to control latency: when the cis-acting immune evasion of
MuHV-4 episome maintenance is bypassed, the lytic
antigen-specific CD8+ T cell population remains small,
as does that responsible for latency ablation (Bennett et al.,
2005). Beta-herpesviruses show a similar discrepancy
between large T cell numbers and effective immunity:
large CD8+ T-cell responses to cytomegalovirus infection
(Khan et al., 2002; Karrer et al., 2003) are not associated
with better control. Limited viral evasion in some cell types
(Hengel et al., 2000) could stimulate CD8+ T cells that
make only a limited contribution to infection control, or
waning CD4+ T-cell control of an earlier checkpoint could
elicit downstream, compensatory responses. Essentially,
large CD8+ T-cell responses to herpesviruses should raise
suspicions of immune inadequacies elsewhere.
Alpha-herpesviruses and T-cell function in the
brain
Our knowledge of T-cell immunity to alpha-herpesviruses
lags somewhat behind that of the beta- and gammaherpesviruses. A particular issue with alpha-herpesviruses
has been whether their latency in neurons mandates
distinct mechanisms of immune control. Many unusual
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P. G. Stevenson, J. P. Simas and S. Efstathiou
phenomena have been reported for T cells in the brain.
However, the only really consistent finding, first reported
for transplantation (Medawar, 1948), has been some
intracerebral immune privilege due to poor priming.
Thus, a viral infection confined to the brain parenchyma
elicits little immune response (Stevenson et al., 1997a).
However, if infection reaches the cerebrospinal fluid or if
priming occurs outside the brain – as it would for HSV –
then the intracerebral infection is readily recognized
(Stevenson et al., 1997b). Neurons have higher thresholds
for MHC class I-restricted epitope presentation than most
other cell types and may resist some pro-apoptotic stimuli,
but antiviral CD8+ T-cell function in the brain does not
seem to be impaired (Stevenson et al., 1997b).
Post-mortem studies of human trigeminal ganglia have
found HSV-specific CD8+ T cells near infected neurons
(Verjans et al., 2007). While the functional importance of
these cells remains unclear, their presence has been taken as
evidence that CD8+ T cells might control neuronal HSV
infection. HSV infection of mice has been used to explore
how this might work. It was assumed early on that a lack of
neuronal MHC class I expression would necessitate HSV
control by a mechanism other than conventional cytotoxicity
(Simmons and Tscharke, 1992). Histological data – the VP16
staining in acutely infected trigeminal ganglia exceeded
subsequent neuronal loss – were consequently interpreted as
non-cytolytic clearance. However, neurons can express MHC
class I (Redwine et al., 2001). Moreover, neurons can express
VP16 with immediate-early kinetics (Thompson et al., 2009),
and infected cell tagging (Proença et al., 2008) has shown that
HSV immediate-early promoters can be active before
neuronal latency is established. Therefore, a loss of VP16
expression need not reflect immune clearance. Non-cytolytic
HSV suppression by granzyme B-mediated degradation of
the ICP4 viral transactivator was recently described
(Knickelbein et al., 2008). However, such a mechanism is
hard to reconcile with the (H2b-restricted) HSV-specific
CD8+ T-cell response focussing on gB, a late lytic gene
(Wallace et al., 1999): by the time gB is made, the need for
ICP4 should have passed. It is also unclear how a murine
enzyme could target a human viral protein while sparing its
normal cellular substrates. Thus, whether CD8+ T cells
might mediate non-cytolytic control of HSV in neurons
remains controversial.
Immune evasion probably limits CD8+ T-cell
recognition of HSV-infected human neurons
Regardless of how HSV-specific CD8+ T cells might act,
can they efficiently recognize HSV-infected human neurons? Alpha-herpesvirus latency classically involves no viral
protein expression and should therefore be inaccessible to
attack by T cells. When reactivation occurs, viral epitopes
can potentially be presented. However, the HSV ICP-47
blocks the TAP peptide transporter (York et al., 1994).
ICP-47 does not block murine TAP (Tomazin et al., 1998)
and introducing a gene capable of inhibiting murine MHC
class I-restricted antigen presentation into HSV significantly impairs CD8+ T-cell-mediated protection (Orr et al.,
2007). These results raise doubt as to whether CD8+ Tcell-mediated control of HSV in mice will translate simply
to humans. Recent data suggest that even in mice, CD4+ T
cells might contribute significantly to HSV control in the
nervous system (Johnson et al., 2008).
Herpesvirus vaccines for naive subjects
Where does herpesvirus immune evasion leave vaccination? Persistent, evasive viruses are clearly not straightforward targets. Disease and transmission will not necessarily
be prevented in the same way, nor will acute and chronic
infection syndromes. Therefore, strategic aims must be
considered.
The best-established herpesvirus vaccines are veterinary:
live-attenuated pseudorabies virus and Marek’s disease
virus (MDV). Both can prevent disease but neither
prevents transmission; this is achieved by quarantine and
culling (Bouma, 2005; Baigent et al., 2006) (Table 4). The
only human herpesvirus vaccine in widespread use is liveattenuated varicella-zoster virus (VZV) (Takahashi, 2001).
This similarly prevents the symptoms of acute infection
(chickenpox), but whether it can prevent the establishment
and transmission of wild-type VZV, and whether the same
approach could be applied to beta- and gamma-herpesviruses, where persistence causes more problems than acute
infection, remain unclear. The other difficulty with
applying the VZV approach more widely is that empirical
attenuation is now considered a significant risk; the
implementation of VZV vaccination was based on safety
testing from 30 years earlier.
Table 4. Herpesvirus vaccines: the problem is transmission
Virus
Pseudorabies virus
MDV
VZV
EBV
MuHV-4
Vaccine
Disease control
Infection control
Live attenuated
Live attenuated
Live attenuated
Gp350
Live attenuated
Yes
Yes
Yes
Unlikely
Unknown
No*
No*
Unknown
No
UnknownD
*Field studies showed reduced but not abolished transmission.
DSuperinfection is reduced but there has been no field test of transmission.
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Journal of General Virology 90
Gamma-herpesvirus immunity – a review
Fig. 1. A schematic view of the gamma-herpesvirus life cycle for MuHV-4. T cells are shown in red, B cells in blue, epithelial
cells in white, neuronal cells are brown and relevant others are in green. Arrows show the movement of virus. Numbers 1–5
indicate definable steps. Key intervention points are latency establishment in naive hosts (steps 2 and 3) and antibody binding to
the virions shed by carriers (step 1). Step 1: virions enter a naive host via secretions such as saliva. MuHV-4 probably enters via
the nose. In vivo entry presents both more opportunities and more challenges than in vitro infection. For example, epithelial
surfaces have an abundant covering of mucus from goblet cells that provides a physical barrier, yet some cells extend cilia
through this. Since virions come from immune carriers, they are likely to have attached antibody. The virions are not normally
neutralized, but neutralization may be possible through boosting fusion-complex-specific antibodies in virus carriers. Nonneutralized MuHV-4 could first infect epithelial cells, IgG Fc receptor-bearing dendritic cells or olfactory neurons. There is no
good evidence for direct B cell infection after a non-invasive inoculation. Step 2: local lytic spread could potentially be targeted
by antiviral drugs or antibody. Latency establishment seems to occur mainly in draining lymph nodes. Infection may reach these
via dendritic cells or via cell-free virions captured by subcapsular sinus macrophages. Step 3: infection next spreads to B cells,
which proliferate. Lytically infected myeloid cells secrete evasion proteins such as the M3 chemokine binding protein to protect
B cells against CD8+ T-cell attack. K3 protects myeloid cells and perhaps also B cells against CD8+ T-cell recognition. IFN-c
produced by CD4+ T cells may limit M3 production and thereby help latent antigen-specific CD8+ T cells to attack B cells.
Step 4: B cells exit germinal centres and differentiate into long-lived, resting memory B cells. Episome maintenance by ORF73
remains below the threshold of antigen presentation. Step 5: virus reactivation probably occurs in submucosal sites,
accompanied by B-cell differentiation to a plasma cell phenotype (Sun & Thorley-Lawson, 2007; Wilson et al., 2007). There
may be further lytic replication in epithelial cells prior to virion shedding. Lytic antigen-specific CD8+ T cells can potentially
inhibit reactivation, but K3 and M3 limit their impact. Consequently, CD4+ T cells seem to protect better against lytic spread.
Gp150 promotes virion release and helps to limit neutralization.
For safety reasons, a recombinant, subunit vaccine would
be preferred. However, viral evasion gives the limited range
of immune effectors primed by such vaccines limited scope
for infection control. Experience with MuHV-4 has borne
this out: lytic antigen-specific CD8+ T cells (Stevenson
et al., 1999c), latent antigen-specific CD8+ T cells
(Usherwood et al., 2001) and gp150 (Stewart et al., 1999)
http://vir.sgmjournals.org
have failed to reduce steady-state latent loads by themselves. Each reduced peak latent loads, but this would seem
unlikely to prevent long-term disease. Only attenuated
whole virus vaccines have reduced long-term latent loads
(Tibbetts et al., 2003; Boname et al., 2004b; Fowler &
Efstathiou, 2004). The best route to an effective gammaherpesvirus vaccine may therefore be genetically targeted
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2325
P. G. Stevenson, J. P. Simas and S. Efstathiou
mutants, backed up by a detailed knowledge of pathogenesis to ensure safety. The most promising MuHV-4 vaccine
to date has been a mutant lacking its ORF73 episome
maintenance protein (Fowler & Efstathiou, 2004). The EBV
equivalent, an EBNA-12 EBNA-22 mutant, should fail to
either persist or transform cells.
Herpesvirus vaccines for virus carriers
Any vaccination strategy must respect the ecology of the
target parasite. Fig. 1 illustrates relevant features of the
gamma-herpesvirus life cycle for MuHV-4. Many details
remain poorly defined, but two distinct hosts are clear:
naive subjects and virus carriers. The viral life cycle could
be interrupted at latency establishment in the former or
transmission from the latter.
MDV illustrates a potential drawback of a vaccine focussed
only on naive subjects. Vaccination protects against disease
but not against wild-type transmission, and the natural
selection for a more transmissible wild-type seems also to
have selected for greater virulence (Biggs, 1997). Therefore,
a useful supplement to reducing herpesvirus latent loads in
naive subjects through live attenuated vaccines would be to
target viral transmission from carriers. MuHV-4 induces
antibody responses that are suboptimal for in vivo
neutralization (Gillet et al., 2007a), in part because the
key neutralization target, the virion membrane fusion
complex, is only weakly immunogenic. Neutralization can
be improved by vaccinating virus carriers with recombinant fusion complex components (Gillet et al., 2007a). Such
an approach could help to eliminate herpesviruses from
populations by reducing the infectivity of carriers.
In summary, the control of herpesvirus infections by
vaccination alone remains a major challenge, principally
because viral immune evasion makes transmission hard to
block. A dual vaccination strategy, distinguishing the need
to protect naive subjects against disease and to reduce the
spread of infection from existing carriers, probably
provides the best chance of eliminating these difficult and
complicated pathogens.
Babcock, G. J., Decker, L. L., Freeman, R. B. & Thorley-Lawson, D. A.
(1999). Epstein–Barr virus-infected resting memory B cells, not
proliferating lymphoblasts, accumulate in the peripheral blood of
immunosuppressed patients. J Exp Med 190, 567–576.
Baigent, S. J., Smith, L. P., Nair, V. K. & Currie, R. J. (2006).
Vaccinal control of Marek’s disease: current challenges, and future
strategies to maximize protection. Vet Immunol Immunopathol 112,
78–86.
Battegay, M., Moskophidis, D., Rahemtulla, A., Hengartner, H., Mak,
T. W. & Zinkernagel, R. M. (1994). Enhanced establishment of a virus
carrier state in adult CD4+ T-cell-deficient mice. J Virol 68, 4700–
4704.
Belz, G. T., Stevenson, P. G., Castrucci, M. R., Altman, J. D. &
Doherty, P. C. (2000). Postexposure vaccination massively increases
the prevalence of gamma-herpesvirus-specific CD8+ T cells but
confers minimal survival advantage on CD4-deficient mice. Proc Natl
Acad Sci U S A 97, 2725–2730.
Belz, G. T., Liu, H., Andreansky, S., Doherty, P. C. & Stevenson, P. G.
(2003). Absence of a functional defect in CD8+ T cells during
primary murine gammaherpesvirus-68 infection of I-Ab2/2 mice.
J Gen Virol 84, 337–341.
Bennett, N. J., May, J. S. & Stevenson, P. G. (2005). Gamma-
herpesvirus latency requires T cell evasion during episome maintenance. PLoS Biol 3, e120.
Biggs, P. M. (1997). Marek’s disease herpesvirus: oncogenesis and
prevention. Philos Trans R Soc Lond B Biol Sci 352, 1951–1962.
Blake, N., Haigh, T., Shaka’a, G., Croom-Carter, D. & Rickinson, A.
(2000). The importance of exogenous antigen in priming the human
CD8+ T cell response: lessons from the EBV nuclear antigen EBNA1.
J Immunol 165, 7078–7087.
Blaskovic, D., Stancekova, M., Svobodova, J. & Mistrikova, J. (1980).
Isolation of five strains of herpesviruses from two species of free living
small rodents. Acta Virol 24, 468.
Boname, J. M. & Stevenson, P. G. (2001). MHC class I ubiquitination
by a viral PHD/LAP finger protein. Immunity 15, 627–636.
Boname, J. M., de Lima, B. D., Lehner, P. J. & Stevenson, P. G.
(2004a). Viral degradation of the MHC class I peptide loading
complex. Immunity 20, 305–317.
Boname, J. M., Coleman, H. M., May, J. S. & Stevenson, P. G.
(2004b). Protection against wild-type murine gammaherpesvirus-68
latency by a latency-deficient mutant. J Gen Virol 85, 131–135.
Bouma, A. (2005). Determination of the effectiveness of Pseudorabies
marker vaccines in experiments and field trials. Biologicals 33,
241–245.
Bowden, R. J., Simas, J. P., Davis, A. J. & Efstathiou, S. (1997).
Murine gammaherpesvirus 68 encodes tRNA-like sequences which
are expressed during latency. J Gen Virol 78, 1675–1687.
Acknowledgements
Work in the authors’ laboratories is supported by the Wellcome Trust
(GR076956MA to P. G. S. and 086403 to S. E.), the UK Medical
Research Council (G0701185 to P. G. S.) and the Fundação para a
Ciência e Tecnologia (POCI/BIA-BCM/60670/2004 to J. P. S.). We
thank Andrew Davison (MRC Virology Unit, Glasgow) for sharing
unpublished data.
References
control of chronic gamma-herpesvirus infection by unconventional
MHC Class Ia-independent CD8 T cells. PLoS Pathog 2, e37.
Bridgeman, A., Stevenson, P. G., Simas, J. P. & Efstathiou, S. (2001).
A secreted chemokine binding protein encoded by murine gammaherpesvirus-68 is necessary for the establishment of a normal latent
load. J Exp Med 194, 301–312.
Burkhardt, A. L., Bolen, J. B., Kieff, E. & Longnecker, R. (1992). An
Adhikary, D., Behrends, U., Moosmann, A., Witter, K., Bornkamm,
G. W. & Mautner, J. (2006). Control of Epstein–Barr virus infection in
vitro by T helper cells specific for virion glycoproteins. J Exp Med 203,
995–1006.
2326
Braaten, D. C., McClellan, J. S., Messaoudi, I., Tibbetts, S. A.,
McClellan, K. B., Nikolich-Zugich, J. & Virgin, H. W. (2006). Effective
Epstein–Barr virus transformation-associated membrane protein
interacts with src family tyrosine kinases. J Virol 66, 5161–5167.
Callan, M. F., Steven, N., Krausa, P., Wilson, J. D., Moss, P. A.,
Gillespie, G. M., Bell, J. I., Rickinson, A. B. & McMichael, A. J. (1996).
Downloaded from www.microbiologyresearch.org by
IP: 88.99.165.207
On: Fri, 16 Jun 2017 20:15:42
Journal of General Virology 90
Gamma-herpesvirus immunity – a review
Large clonal expansions of CD8+ T cells in acute infectious
mononucleosis. Nat Med 2, 906–911.
Cardin, R. D., Brooks, J. W., Sarawar, S. R. & Doherty, P. C. (1996).
Progressive loss of CD8+ T cell-mediated control of a gammaherpesvirus in the absence of CD4+ T cells. J Exp Med 184, 863–871.
Fu, T., Voo, K. S. & Wang, R. F. (2004). Critical role of EBNA1-specific
CD4+ T cells in the control of mouse Burkitt lymphoma in vivo. J Clin
Invest 114, 542–550.
Gangappa, S., Kapadia, S. B., Speck, S. H. & Virgin, H. W. (2002).
Carneiro-Sampaio, M. & Coutinho, A. (2007). Immunity to microbes:
Antibody to a lytic cycle viral protein decreases gammaherpesvirus
latency in B-cell-deficient mice. J Virol 76, 11460–11468.
lessons from primary immunodeficiencies. Infect Immun 75, 1545–
1555.
Gill, M. B., Gillet, L., Colaco, S., May, J. S., de Lima, B. D. &
Stevenson, P. G. (2006). Murine gammaherpesvirus-68 glycoprotein
Cerundolo, V. & de la Salle, H. (2006). Description of HLA class I-
H-glycoprotein L complex is a major target for neutralizing
monoclonal antibodies. J Gen Virol 87, 1465–1475.
and CD8-deficient patients: insights into the function of cytotoxic T
lymphocytes and NK cells in host defense. Semin Immunol 18, 330–
336.
Chastel, C., Beaucournu, J. P., Chastel, O., Legrand, M. C. & Le Goff, F.
(1994). A herpesvirus from an European shrew (Crocidura russula).
Gill, M. B., Wright, D. E., Smith, C. M., May, J. S. & Stevenson, P. G.
(2009). Murid herpesvirus-4 lacking thymidine kinase reveals route-
dependent requirements for host colonization. J Gen Virol 90, 1461–
1470.
Acta Virol 38, 309.
Gillet, L. & Stevenson, P. G. (2007a). Evidence for a multiprotein
Christensen, J. P., Cardin, R. D., Branum, K. C. & Doherty, P. C.
(1999). CD4+ T cell-mediated control of a gamma-herpesvirus in B
cell-deficient mice is mediated by IFN-c. Proc Natl Acad Sci U S A 96,
Gillet, L. & Stevenson, P. G. (2007b). Antibody evasion by the N
5135–5140.
Coleman, H. M., Brierley, I. & Stevenson, P. G. (2003a). An internal
ribosome entry site directs translation of the murine gammaherpesvirus 68 MK3 open reading frame. J Virol 77, 13093–13105.
Coleman, H. M., de Lima, B., Morton, V. & Stevenson, P. G. (2003b).
gamma-2 herpesvirus entry complex. J Virol 81, 13082–13091.
terminus of murid herpesvirus-4 glycoprotein B. EMBO J 26, 5131–
5142.
Gillet, L., Gill, M. B., Colaco, S., Smith, C. M. & Stevenson, P. G.
(2006). Murine gammaherpesvirus-68 glycoprotein B presents a
difficult neutralization target to monoclonal antibodies derived from
infected mice. J Gen Virol 87, 3515–3527.
Murine gammaherpesvirus 68 lacking thymidine kinase shows severe
attenuation of lytic cycle replication in vivo but still establishes
latency. J Virol 77, 2410–2417.
Gillet, L., May, J. S. & Stevenson, P. G. (2007a). Post-exposure
Davenport, M. G. & Pagano, J. S. (1999). Expression of EBNA-1
Gillet, L., May, J. S., Colaco, S. & Stevenson, P. G. (2007b). The
vaccination improves gammaherpesvirus neutralization. PLoS One 2,
e899.
mRNA is regulated by cell cycle during Epstein–Barr virus type I
latency. J Virol 73, 3154–3161.
murine gammaherpesvirus-68 gp150 acts as an immunogenic decoy
to limit virion neutralization. PLoS One 2, e705.
de Lima, B. D., May, J. S. & Stevenson, P. G. (2004). Murine
Gillet, L., Colaco, S. & Stevenson, P. G. (2008a). Glycoprotein B
gammaherpesvirus 68 lacking gp150 shows defective virion release
but establishes normal latency in vivo. J Virol 78, 5103–5112.
switches conformation during murid herpesvirus 4 entry. J Gen Virol
89, 1352–1363.
de Lima, B. D., May, J. S., Marques, S., Simas, J. P. & Stevenson, P. G.
(2005). Murine gammaherpesvirus 68 bcl-2 homologue contributes to
Gillet, L., Colaco, S. & Stevenson, P. G. (2008b). The murid
latency establishment in vivo. J Gen Virol 86, 31–40.
herpesvirus-4 gL regulates an entry-associated conformation change
in gH. PLoS One 3, e2811.
Dutia, B. M., Clarke, C. J., Allen, D. J. & Nash, A. A. (1997).
Gillet, L., May, J. S. & Stevenson, P. G. (2009a). In vivo importance of
Pathological changes in the spleens of gamma interferon receptordeficient mice infected with murine gammaherpesvirus: a role for
CD8 T cells. J Virol 71, 4278–4283.
Ehtisham, S., Sunil-Chandra, N. P. & Nash, A. A. (1993). Pathogenesis
of murine gammaherpesvirus infection in mice deficient in CD4 and
CD8 T cells. J Virol 67, 5247–5252.
Elliott, S. L., Suhrbier, A., Miles, J. J., Lawrence, G., Pye, S. J., Le, T. T.,
Rosenstengel, A., Nguyen, T., Allworth, A. & other authors (2008).
+
heparan sulfate-binding glycoproteins for murid herpesvirus-4
infection. J Gen Virol 90, 602–613.
Gillet, L., Alenquer, M., Glauser, D. L., Colaco, S., May, J. S. &
Stevenson, P. G. (2009b). Glycoprotein L sets the neutra-
lization profile of murid herpesvirus-4. J Gen Virol 90, 1202–
1214.
Gottschalk, S., Rooney, C. M. & Heslop, H. E. (2005). Post-transplant
lymphoproliferative disorders. Annu Rev Med 56, 29–44.
Phase I trial of a CD8 T-cell peptide epitope-based vaccine for
infectious mononucleosis. J Virol 82, 1448–1457.
Hadinoto, V., Shapiro, M., Greenough, T. C., Sullivan, J. L., Luzuriaga, K.
& Thorley-Lawson, D. A. (2008). On the dynamics of acute EBV
Epstein, M. A., Achong, B. G. & Barr, Y. M. (1964). Virus particles
infection and the pathogenesis of infectious mononucleosis. Blood 111,
1420–1427.
in cultured lymphoblasts from Burkitt’s lymphoma. Lancet 1, 702–
703.
Faulkner, G. C., Krajewski, A. S. & Crawford, D. H. (2000). The ins
and outs of EBV infection. Trends Microbiol 8, 185–189.
Fowler, P. & Efstathiou, S. (2004). Vaccine potential of a murine
gammaherpesvirus-68 mutant deficient for ORF73. J Gen Virol 85,
609–613.
Fowler, P., Marques, S., Simas, J. P. & Efstathiou, S. (2003). ORF73
Haque, T., Wilkie, G. M., Jones, M. M., Higgins, C. D., Urquhart, G.,
Wingate, P., Burns, D., McAulay, K., Turner, M. & other authors
(2007). Allogeneic cytotoxic T-cell therapy for EBV-positive post-
transplantation lymphoproliferative disease: results of a phase 2
multicenter clinical trial. Blood 110, 1123–1131.
Hayashida, I., Nagafuchi, S., Hayashi, Y., Kino, Y., Mori, R., Oda, H.,
Ohtomo, N. & Tashiro, A. (1982). Mechanism of antibody-mediated
of murine herpesvirus-68 is critical for the establishment and
maintenance of latency. J Gen Virol 84, 3405–3416.
protection against herpes simplex virus infection in athymic nude
mice: requirement of Fc portion of antibody. Microbiol Immunol 26,
497–509.
Früh, K., Bartee, E., Gouveia, K. & Mansouri, M. (2002). Immune
Hengel, H., Brune, W. & Koszinowski, U. H. (1998). Immune evasion
evasion by a novel family of viral PHD/LAP-finger proteins of
gamma-2 herpesviruses and poxviruses. Virus Res 88, 55–69.
by cytomegalovirus – survival strategies of a highly adapted
opportunist. Trends Microbiol 6, 190–197.
http://vir.sgmjournals.org
Downloaded from www.microbiologyresearch.org by
IP: 88.99.165.207
On: Fri, 16 Jun 2017 20:15:42
2327
P. G. Stevenson, J. P. Simas and S. Efstathiou
Hengel, H., Reusch, U., Geginat, G., Holtappels, R., Ruppert, T.,
Hellebrand, E. & Koszinowski, U. H. (2000). Macrophages escape
infection and the establishment of viral latency in mice. J Virol 73,
9849–9857.
inhibition of major histocompatibility complex class I-dependent
antigen presentation by cytomegalovirus. J Virol 74, 7861–7868.
Lybarger, L., Wang, X., Harris, M. R., Virgin, H. W. & Hansen, T. H.
(2003). Virus subversion of the MHC class I peptide-loading
Hislop, A. D., Ressing, M. E., van Leeuwen, D., Pudney, V. A., Horst, D.,
Koppers-Lalic, D., Croft, N. P., Neefjes, J. J., Rickinson, A. B. & Wiertz,
E. J. H. J. (2007). A CD8+ T cell immune evasion protein specific to
Marques, S., Efstathiou, S., Smith, K. G., Haury, M. & Simas, J. P.
(2003). Selective gene expression of latent murine gammaherpesvirus
Epstein–Barr virus and its close relatives in Old World primates. J Exp
Med 204, 1863–1873.
complex. Immunity 18, 121–130.
68 in B lymphocytes. J Virol 77, 7308–7318.
Marques, S., Alenquer, M., Stevenson, P. G. & Simas, J. P. (2008). A
mononucleosis. Am J Public Health Nations Health 54, 1699–1705.
single CD8+ T cell epitope sets the long-term latent load of a murid
herpesvirus. PLoS Pathog 4, e1000177.
Husain, S. M., Usherwood, E. J., Dyson, H., Coleclough, C., Coppola,
M. A., Woodland, D. L., Blackman, M. A., Stewart, J. P. & Sample, J. T.
(1999). Murine gammaherpesvirus M2 gene is latency-associated and
Mautner, J., Pich, D., Nimmerjahn, F., Milosevic, S., Adhikary, D.,
Christoph, H., Witter, K., Bornkamm, G. W., Hammerschmidt, W. &
Behrends, U. (2004). Epstein–Barr virus nuclear antigen 1 evades
Hoagland, R. J. (1964). The incubation period of infectious
its protein a target for CD8+ T lymphocytes. Proc Natl Acad Sci U S A
96, 7508–7513.
direct immune recognition by CD4+ T helper cells. Eur J Immunol
34, 2500–2509.
Janz, A., Oezel, M., Kurzeder, C., Mautner, J., Pich, D., Kost, M.,
Hammerschmidt, W. & Delecluse, H. J. (2000). Infectious Epstein–
McClellan, J. S., Tibbetts, S. A., Gangappa, S., Brett, K. A. & Virgin,
H. W. (2004). Critical role of CD4 T cells in an antibody-independent
Barr virus lacking major glycoprotein BLLF1 (gp350/220) demonstrates the existence of additional viral ligands. J Virol 74, 10142–
10152.
mechanism of vaccination against gammaherpesvirus latency. J Virol
78, 6836–6845.
Johnson, A. J., Chu, C. F. & Milligan, G. N. (2008). Effector CD4+ T-
Medawar, P. B. (1948). Immunity to homologous grafted skin: the
cell involvement in clearance of infectious herpes simplex virus type 1
from sensory ganglia and spinal cords. J Virol 82, 9678–9688.
fate of skin homografts transplanted to the brain, to subcutaneous
tissue, and to the anterior chamber of the eye. Br J Exp Pathol 29,
58–69.
Karrer, U., Sierro, S., Wagner, M., Oxenius, A., Hengel, H.,
Koszinowski, U. H., Phillips, R. E. & Klenerman, P. (2003).
Milho, R., Smith, C. M., Marques, S., Alenquer, M., May, J. S., Gillet, L.,
Gaspar, M., Efstathiou, S., Simas, J. P. & Stevenson, P. G. (2009). In
Memory inflation: continuous accumulation of antiviral CD8+ T
cells over time. J Immunol 170, 2022–2029.
Kayhan, B., Yager, E. J., Lanzer, K., Cookenham, T., Jia, Q., Wu, T. T.,
Woodland, D. L., Sun, R. & Blackman, M. A. (2007). A replication-
deficient murine gamma-herpesvirus blocked in late viral gene
expression can establish latency and elicit protective cellular
immunity. J Immunol 179, 8392–8402.
vivo imaging of murid herpesvirus-4 infection. J Gen Virol 90, 21–32.
Moorman, N. J., Willer, D. O. & Speck, S. H. (2003). The
gammaherpesvirus 68 latency-associated nuclear antigen homolog is
critical for the establishment of splenic latency. J Virol 77, 10295–
10303.
Moser, J. M., Farrell, M. L., Krug, L. T., Upton, J. W. & Speck, S. H.
(2006). A gammaherpesvirus 68 gene 50 null mutant establishes long-
Khan, N., Shariff, N., Cobbold, M., Bruton, R., Ainsworth, J. A.,
Sinclair, A. J., Nayak, L. & Moss, P. A. (2002). Cytomegalovirus
term latency in the lung but fails to vaccinate against a wild-type virus
challenge. J Virol 80, 1592–1598.
seropositivity drives the CD8 T cell repertoire toward greater clonality
in healthy elderly individuals. J Immunol 169, 1984–1992.
Nash, A. A., Dutia, B. M., Stewart, J. P. & Davison, A. J. (2001).
Kim, I. J., Flaño, E., Woodland, D. L. & Blackman, M. A. (2002).
Natural history of murine gamma-herpesvirus infection. Philos Trans
R Soc Lond B Biol Sci 356, 569–579.
Antibody-mediated control of persistent gamma-herpesvirus infection. J Immunol 168, 3958–3964.
Nicholas, J. (2005). Human gammaherpesvirus cytokines and
Klein, R. J. (1982). Treatment of experimental latent herpes simplex
Nikiforow, S., Bottomly, K., Miller, G. & Munz, C. (2003). Cytolytic
chemokine receptors. J Interferon Cytokine Res 25, 373–383.
virus infections with acyclovir and other antiviral compounds. Am J
Med 73, 138–142.
CD4+-T-cell clones reactive to EBNA1 inhibit Epstein–Barr virusinduced B-cell proliferation. J Virol 77, 12088–12104.
Knickelbein, J. E., Khanna, K. M., Yee, M. B., Baty, C. J., Kinchington,
P. R. & Hendricks, R. L. (2008). Noncytotoxic lytic granule-mediated
Orr, M. T., Mathis, M. A., Lagunoff, M., Sacks, J. A. & Wilson, C. B.
(2007). CD8 T cell control of HSV reactivation from latency is
CD8+ T cell inhibition of HSV-1 reactivation from neuronal latency.
Science 322, 268–271.
abrogated by viral inhibition of MHC class I. Cell Host Microbe 2,
172–180.
Kozuch, O., Reichel, M., Lesso, J., Remenova, A., Labuda, M., Lysy, J.
& Mistrikova, J. (1993). Further isolation of murine herpesviruses
Parry, C. M., Simas, J. P., Smith, V. P., Stewart, C. A., Minson, A. C.,
Efstathiou, S. & Alcami, A. (2000). A broad spectrum secreted
from small mammals in southwestern Slovakia. Acta Virol 37, 101–
105.
chemokine binding protein encoded by a herpesvirus. J Exp Med 191,
573–578.
Lee, H., Guo, J., Li, M., Choi, J. K., DeMaria, M., Rosenzweig, M. &
Jung, J. U. (1998). Identification of an immunoreceptor tyrosine-
Polić, B., Jonjić, S., Pavić, I., Crnković, I., Zorica, I., Hengel, H.,
Lucin, P. & Koszinowski, U. H. (1996). Lack of MHC class I complex
based activation motif of K1 transforming protein of Kaposi’s
sarcoma-associated herpesvirus. Mol Cell Biol 18, 5219–5228.
expression has no effect on spread and control of cytomegalovirus
infection in vivo. J Gen Virol 77, 217–225.
Levitskaya, J., Coram, M., Levitsky, V., Imreh, S., SteigerwaldMullen, P. M., Klein, G., Kurilla, M. G. & Masucci, M. G. (1995).
Polić, B., Hengel, H., Krmpotić, A., Trgovcich, J., Pavić, I., Luccaronin, P.,
Jonjić, S. & Koszinowski, U. H. (1998). Hierarchical and redundant
Inhibition of antigen processing by the internal repeat region of the
Epstein–Barr virus nuclear antigen-1. Nature 375, 685–688.
lymphocyte subset control precludes cytomegalovirus replication during
latent infection. J Exp Med 188, 1047–1054.
Liu, L., Usherwood, E. J., Blackman, M. A. & Woodland, D. L.
(1999). T-cell vaccination alters the course of murine herpesvirus 68
Proença, J. T., Coleman, H. M., Connor, V., Winton, D. J. & Efstathiou, S.
(2008). A historical analysis of herpes simplex virus promoter activation
2328
Downloaded from www.microbiologyresearch.org by
IP: 88.99.165.207
On: Fri, 16 Jun 2017 20:15:42
Journal of General Virology 90
Gamma-herpesvirus immunity – a review
in vivo reveals distinct populations of latently infected neurones. J Gen
Virol 89, 2965–2974.
Sparks-Thissen, R. L., Braaten, D. C., Hildner, K., Murphy, T. L.,
Murphy, K. M. & Virgin, H. W. (2005). CD4 T cell control of acute and
Reddehase, M. J., Simon, C. O., Seckert, C. K., Lemmermann, N. &
Grzimek, N. K. (2008). Murine model of cytomegalovirus latency and
latent murine gammaherpesvirus infection requires IFN gamma.
Virology 338, 201–208.
reactivation. Curr Top Microbiol Immunol 325, 315–331.
Stebbing, J., Bourboulia, D., Johnson, M., Henderson, S., Williams, I.,
Wilder, N., Tyrer, M., Youle, M., Imami, N. & other authors (2003).
Redwine, J. M., Buchmeier, M. J. & Evans, C. F. (2001). In vivo
expression of major histocompatibility complex molecules on
oligodendrocytes and neurons during viral infection. Am J Pathol
159, 1219–1224.
Kaposi’s sarcoma-associated herpesvirus cytotoxic T lymphocytes
recognize and target Darwinian positively selected autologous K1
epitopes. J Virol 77, 4306–4314.
Rice, J., de Lima, B., Stevenson, F. K. & Stevenson, P. G. (2002). A
Steed, A., Buch, T., Waisman, A. & Virgin, H. W. (2007). Gamma
gamma-herpesvirus immune evasion gene allows tumor cells in vivo
to escape attack by cytotoxic T cells specific for a tumor epitope. Eur J
Immunol 32, 3481–3487.
Stevenson, P. G. (2004). Immune evasion by gamma-herpesviruses.
Rickinson, A. B. & Moss, D. J. (1997). Human cytotoxic T lymphocyte
responses to Epstein–Barr virus infection. Annu Rev Immunol 15,
405–431.
interferon blocks gammaherpesvirus reactivation from latency in a
cell type-specific manner. J Virol 81, 6134–6140.
Curr Opin Immunol 16, 456–462.
Stevenson, P. G. & Efstathiou, S. (2005). Immune mechanisms in
murine gammaherpesvirus-68 infection. Viral Immunol 18, 445–
456.
Rodrigues, L., Pires de Miranda, M., Caloca, M. J., Bustelo, X. R. &
Simas, J. P. (2006). Activation of Vav by the gammaherpesvirus M2
Stevenson, P. G., Hawke, S., Sloan, D. J. & Bangham, C. R. (1997a).
protein contributes to the establishment of viral latency in B
lymphocytes. J Virol 80, 6123–6135.
The immunogenicity of intracerebral virus infection depends on
anatomical site. J Virol 71, 145–151.
Rosa, G. T., Gillet, L., Smith, C. M., de Lima, B. D. & Stevenson, P. G.
(2007). IgG Fc receptors provide an alternative infection route for
Stevenson, P. G., Bangham, C. R. & Hawke, S. (1997b). Recruitment,
murine gamma-herpesvirus-68. PLoS One 2, e560.
activation and proliferation of CD8+ memory T cells in an
immunoprivileged site. Eur J Immunol 27, 3259–3268.
Roughan, J. E. & Thorley-Lawson, D. A. (2009). The intersection of
Stevenson, P. G., Belz, G. T., Altman, J. D. & Doherty, P. C. (1998).
Epstein–Barr virus with the germinal center. J Virol 83, 3968–
3976.
Sample, J., Henson, E. B. & Sample, C. (1992). The Epstein–Barr
virus nuclear protein 1 promoter active in type I latency is
autoregulated. J Virol 66, 4654–4661.
Sarawar, S. R., Cardin, R. D., Brooks, J. W., Mehrpooya, M.,
Hamilton-Easton, A. M., Mo, X. Y. & Doherty, P. C. (1997). Gamma
interferon is not essential for recovery from acute infection with
murine gammaherpesvirus 68. J Virol 71, 3916–3921.
Shannon-Lowe, C. D., Neuhierl, B., Baldwin, G., Rickinson, A. B. &
Delecluse, H. J. (2006). Resting B cells as a transfer vehicle for
Epstein–Barr virus infection of epithelial cells. Proc Natl Acad Sci U S A
103, 7065–7070.
Simmons, A. & Tscharke, D. C. (1992). Anti-CD8 impairs clearance
of herpes simplex virus from the nervous system: implications for the
fate of virally infected neurons. J Exp Med 175, 1337–1344.
Skehel, J. J. & Wiley, D. C. (2000). Receptor binding and membrane
fusion in virus entry: the influenza hemagglutinin. Annu Rev Biochem
69, 531–569.
Smith, C. M., Rosa, G. T., May, J. S., Bennett, N. J., Mount, A. M., Belz,
G. T. & Stevenson, P. G. (2006). CD4+ T cells specific for a model
latency-associated antigen fail to control a gammaherpesvirus in vivo.
Eur J Immunol 36, 3186–3197.
Smith, C. M., Gill, M. B., May, J. S. & Stevenson, P. G. (2007). Murine
gammaherpesvirus-68 inhibits antigen presentation by dendritic cells.
PLoS One 2, e1048.
Sokal, E. M., Hoppenbrouwers, K., Vandermeulen, C., Moutschen, M.,
Léonard, P., Moreels, A., Haumont, M., Bollen, A., Smets, F. &
Denis, M. (2007). Recombinant gp350 vaccine for infectious mono-
Virus-specific CD8+ T cell numbers are maintained during gammaherpesvirus reactivation in CD4-deficient mice. Proc Natl Acad Sci
U S A 95, 15565–15570.
Stevenson, P. G., Cardin, R. D., Christensen, J. P. & Doherty, P. C.
(1999a). Immunological control of a murine gammaherpesvirus
independent of CD8+ T cells. J Gen Virol 80, 477–483.
Stevenson, P. G., Belz, G. T., Altman, J. D. & Doherty, P. C. (1999b).
Changing patterns of dominance in the CD8+ T cell response during
acute and persistent murine gamma-herpesvirus infection. Eur J
Immunol 29, 1059–1067.
Stevenson, P. G., Belz, G. T., Castrucci, M. R., Altman, J. D. &
Doherty, P. C. (1999c). A gamma-herpesvirus sneaks through a
CD8+ T cell response primed to a lytic-phase epitope. Proc Natl Acad
Sci U S A 96, 9281–9286.
Stevenson, P. G., May, J. S., Smith, X. G., Marques, S., Adler, H.,
Koszinowski, U. H., Simas, J. P. & Efstathiou, S. (2002). K3-mediated
evasion of CD8+ T cells aids amplification of a latent gammaherpesvirus. Nat Immunol 3, 733–740.
Stewart, J. P., Micali, N., Usherwood, E. J., Bonina, L. & Nash, A. A.
(1999). Murine gamma-herpesvirus 68 glycoprotein 150 protects
against virus-induced mononucleosis: a model system for gammaherpesvirus vaccination. Vaccine 17, 152–157.
Sun, C. C. & Thorley-Lawson, D. A. (2007). Plasma cell-specific
transcription factor XBP-1s binds to and transactivates the Epstein–
Barr virus BZLF1 promoter. J Virol 81, 13566–13577.
Takahashi, M. (2001). 25 years’ experience with the Biken Oka strain
varicella vaccine: a clinical overview. Paediatr Drugs 3, 285–292.
Tarakanova, V. L., Suarez, F., Tibbetts, S. A., Jacoby, M. A., Weck,
K. E., Hess, J. L., Speck, S. H. & Virgin, H. W. (2005). Murine
gammaherpesvirus 68 infection is associated with lymphoproliferative
disease and lymphoma in BALB b2 microglobulin-deficient mice.
J Virol 79, 14668–14679.
nucleosis: a phase 2, randomized, double-blind, placebo-controlled
trial to evaluate the safety, immunogenicity, and efficacy of an
Epstein–Barr virus vaccine in healthy young adults. J Infect Dis 196,
1749–1753.
Thompson, R. L., Preston, C. M. & Sawtell, N. M. (2009). De novo
Sparks-Thissen, R. L., Braaten, D. C., Kreher, S., Speck, S. H. &
Virgin, H. W. (2004). An optimized CD4 T-cell response can control
synthesis of VP16 coordinates the exit from HSV latency in vivo. PLoS
Pathog 5, e1000352.
productive and latent gammaherpesvirus infection. J Virol 78, 6827–
6835.
Thomsen, A. R., Johansen, J., Marker, O. & Christensen, J. P. (1996).
http://vir.sgmjournals.org
Exhaustion of CTL memory and recrudescence of viremia in
Downloaded from www.microbiologyresearch.org by
IP: 88.99.165.207
On: Fri, 16 Jun 2017 20:15:42
2329
P. G. Stevenson, J. P. Simas and S. Efstathiou
lymphocytic choriomeningitis virus-infected MHC class II-deficient
mice and B cell-deficient mice. J Immunol 157, 3074–3080.
Thorley-Lawson, D. A. (2001). Epstein–Barr virus: exploiting the
immune system. Nat Rev Immunol 1, 75–82.
Thorley-Lawson, D. A. & Geilinger, K. (1980). Monoclonal antibodies
Virgin, H. W. & Speck, S. H. (1999). Unravelling immunity to gammaherpesviruses: a new model for understanding the role of immunity in
chronic virus infection. Curr Opin Immunol 11, 371–379.
Virgin, H. W., Latreille, P., Wamsley, P., Hallsworth, K., Weck, K. E.,
Dal Canto, A. J. & Speck, S. H. (1997). Complete sequence and
against the major glycoprotein (gp350/220) of Epstein–Barr virus
neutralize infectivity. Proc Natl Acad Sci U S A 77, 5307–5311.
genomic analysis of murine gammaherpesvirus 68. J Virol 71, 5894–
5904.
Tibbetts, S. A., van Dyk, L. F., Speck, S. H. & Virgin, H. W. (2002).
Voo, K. S., Fu, T., Wang, H. Y., Tellam, J., Heslop, H. E., Brenner, M. K.,
Rooney, C. M. & Wang, R. F. (2004). Evidence for the presentation of
Immune control of the number and reactivation phenotype of cells
latently infected with a gammaherpesvirus. J Virol 76, 7125–7132.
Tibbetts, S. A., McClellan, J. S., Gangappa, S., Speck, S. H. & Virgin,
H. W. (2003). Effective vaccination against long-term gammaherpes-
virus latency. J Virol 77, 2522–2529.
Tibbetts, S. A., Suarez, F., Steed, A. L., Simmons, J. A. & Virgin, H. W.
(2006). A gamma-herpesvirus deficient in replication establishes
chronic infection in vivo and is impervious to restriction by adaptive
immune cells. Virology 353, 210–219.
Tomazin, R., van Schoot, N. E., Goldsmith, K., Jugovic, P., Sempé, P.,
Früh, K. & Johnson, D. C. (1998). Herpes simplex virus type 2 ICP47
inhibits human TAP but not mouse TAP. J Virol 72, 2560–2563.
major histocompatibility complex class I-restricted Epstein–Barr virus
nuclear antigen 1 peptides to CD8+ T lymphocytes. J Exp Med 199,
459–470.
Wallace, M. E., Keating, R., Heath, W. R. & Carbone, F. R. (1999). The
cytotoxic T-cell response to herpes simplex virus type 1 infection of
C57BL/6 mice is almost entirely directed against a single immunodominant determinant. J Virol 73, 7619–7626.
Weck, K. E., Dal Canto, A. J., Gould, J. D., O’Guin, A. K., Roth, K. A.,
Saffitz, J. E., Speck, S. H. & Virgin, H. W. (1997). Murine gamma-
herpesvirus 68 causes severe large-vessel arteritis in mice lacking
interferon-gamma responsiveness: a new model for virus-induced
vascular disease. Nat Med 3, 1346–1353.
Topham, D. J. & Doherty, P. C. (1998). Clearance of an influenza A
Wilson, S. J., Tsao, E. H., Webb, B. L., Ye, H., Dalton-Griffin, L.,
Tsantoulas, C., Gale, C. V., Du, M. Q., Whitehouse, A. & Kellam, P.
(2007). X box binding protein XBP-1s transactivates the Kaposi’s
Turner, A., Bruun, B., Minson, T. & Browne, H. (1998). Glycoproteins
sarcoma-associated herpesvirus (KSHV) ORF50 promoter, linking
plasma cell differentiation to KSHV reactivation from latency. J Virol
81, 13578–13586.
virus by CD4+ T cells is inefficient in the absence of B cells. J Virol 72,
882–885.
gB, gD, and gHgL of herpes simplex virus type 1 are necessary and
sufficient to mediate membrane fusion in a Cos cell transfection
system. J Virol 72, 873–875.
Usherwood, E. J., Ross, A. J., Allen, D. J. & Nash, A. A. (1996). Murine
gammaherpesvirus-induced splenomegaly: a critical role for CD4 T
cells. J Gen Virol 77, 627–630.
Usherwood, E. J., Ward, K. A., Blackman, M. A., Stewart, J. P. &
Woodland, D. L. (2001). Latent antigen vaccination in a model
gammaherpesvirus infection. J Virol 75, 8283–8288.
Yao, Q. Y., Ogan, P., Rowe, M., Wood, M. & Rickinson, A. B. (1989a).
The Epstein–Barr virus: host balance in acute infectious mononucleosis patients receiving acyclovir anti-viral therapy. Int J Cancer 43,
61–66.
Yao, Q. Y., Ogan, P., Rowe, M., Wood, M. & Rickinson, A. B. (1989b).
Epstein–Barr virus-infected B cells persist in the circulation of
acyclovir-treated virus carriers. Int J Cancer 43, 67–71.
Usherwood, E. J., Meadows, S. K., Crist, S. G., Bellfy, S. C. &
Sentman, C. L. (2005). Control of murine gammaherpesvirus
Yewdell, J. W. & Hill, A. B. (2002). Viral interference with antigen
infection is independent of NK cells. Eur J Immunol 35, 2956–
2961.
Yin, Y., Manoury, B. & Fahraeus, R. (2003). Self-inhibition of
van Berkel, V., Barrett, J., Tiffany, H. L., Fremont, D. H., Murphy, P. M.,
McFadden, G., Speck, S. H. & Virgin, H. W. (2000). Identification of a
gammaherpesvirus selective chemokine binding protein that inhibits
chemokine action. J Virol 74, 6741–6747.
Verjans, G. M., Hintzen, R. Q., van Dun, J. M., Poot, A., Milikan, J. C.,
Laman, J. D., Langerak, A. W., Kinchington, P. R. & Osterhaus, A. D.
(2007). Selective retention of herpes simplex virus-specific T cells in
latently infected human trigeminal ganglia. Proc Natl Acad Sci U S A
104, 3496–3501.
2330
presentation. Nat Immunol 3, 1019–1025.
synthesis and antigen presentation by Epstein–Barr virus-encoded
EBNA1. Science 301, 1371–1374.
York, I. A., Roop, C., Andrews, D. W., Riddell, S. R., Graham, F. L. &
Johnson, D. C. (1994). A cytosolic herpes simplex virus protein
inhibits antigen presentation to CD8+ T lymphocytes. Cell 77, 525–
535.
Zinkernagel, R. M. & Hengartner, H. (2006). Protective ‘immunity’ by
pre-existent neutralizing antibody titers and preactivated T cells but
not by so-called ‘immunological memory’. Immunol Rev 211, 310–
319.
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