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Titulares
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Herpesvirus 7
Human Herpesvirus 7 in Dermatology
What Role Does it Play?
Werner Kempf
Department of Dermatology, University Hospital, Zurich, Switzerland
Abstract Human herpesvirus 7 (HHV-7) was discovered in 1989 as a new member of the ?-herpesvirus
subfamily.
Primary infection occurs early in life and manifests as exanthema subitum, or other febrile
illnesses mimicking
measles and rubella. Thus, HHV-7 has to be considered as a causative agent in a variety of
macular-papular
rashes in children. In addition, HHV-7 was found in some cases of other inflammatory skin
disorders, such as
psoriasis. There are controversial data on the detection of HHV-7 in pityriasis rosea, but so far
there is not enough
evidence for a pathogenetic association of HHV-7 with this exanthematic skin disease. Although
HHV-7 can be
found in some cases of Hodgkin?s disease, there are no data supporting a direct causative role in
this lymphoma
type nor in other nodal or primary cutaneous lymphomas. In various epidemiologic forms of
Kaposi?s sarcoma,
infection of monocytic cells with HHV-7 was demonstrated, which may indirectly influence tumor
biology. In
the context of immunosuppression, HHV-7 has recently been identified as an emerging pathogen in
transplant
recipients and may exacerbate graft rejection in renal transplant recipients. The ability of
HHV-7 to induce
cytokine production in infected cells could make HHV-7 an important pathogenetic co-factor in
inflammatory
and neoplastic disorders. Moreover, the restricted cellular tropism of HHV-7 may render this
virus an interesting
vector for gene therapy. Thirteen years after the discovery of HHV-7, there has been considerable
progress in
characterizing its genetic structure, virus-induced effects on infected host cells and in the
development of
diagnostic tools. Nevertheless, the role of HHV-7 in various skin diseases and the clinical
manifestations of
reactivation of HHV-7 infection have still to be defined.
LEADING ARTICLE Am J Clin Dermatol 2002; 3 (5): 309-315
1175-0561/02/0005-0309/$25.00/0
© Adis International Limited. All rights reserved.
During the last 3 decades, three new human herpesviruses
have been discovered. Two of these, human herpesvirus 6 (HHV-
6) and human herpesvirus 7 (HHV-7), are closely related to cytomegalovirus
(CMV) and constitute the Roseolovirus genus of the
?-herpesvirus subfamily (for a review see Black & Pellett[1]).
Similar to other human herpesviruses, infections with HHV-6 and
HHV-7 can manifest with cutaneous involvement. Exanthema
subitum and other childhood rashes were shown to be clinical
manifestations of primary infection.[2-4] Recently, HHV-7 was
suggested to be a causative cofactor in pityriasis rosea and other
inflammatory skin disorders. In addition, HHV-7 has been detected
in neoplasms, such as Kaposi?s sarcoma and lymphoproliferative
disorders. To date, more than 300 publications on
HHV-7 have been published and are listed in Index Medicus/
Medline. For this review, we have selected mostly original
papers for discussion, in particular publications providing epidemiologic
and experimental data on HHV-7 in skin diseases. This
review aims to provide information on the biology of HHV-7, to
summarize the data on its presence and the putative role of HHV-7
in various inflammatory and neoplastic skin diseases.
1. The Biology of Human Herpesvirus 7 (HHV-7)
In 1989, Frenkel et al.[5] isolated a new herpesvirus, which
was designated as HHV-7, from activated peripheral blood lymphocytes
(PBL) of a healthy individual. Genetically, it is closely
related to human herpesvirus 6A, human herpesvirus 6B (HHV-
6B) and CMV, with sequence homologies of up to 75%.[6] The
genome of 145-kB was cloned and encodes approximately 80
genes.[7,8] Various strains of HHV-7 were identified, which differ
mainly in regard to virus growth in different cell cultures.[9,10]
HHV-7 is still, even 13 years after its discovery, a little-studied
herpesvirus, which is in part because of its restricted growth in
cultured cells. So far, HHV-7 can only be propagated in vitro, in
cord blood lymphocytes, activated T cells and in SupT1 cells
(lymphoblastoid T cell line),[11,12] but viral replication remains
low even under optimized conditions.
? This manuscript is dedicated to Prof. Gabriella Campadelli Fiume, University of Bologna,
Bologna, Italy.
HHV-7 uses the CD4 molecule as a critical component of
the cellular membrane receptor.[13] Synthesis and expression of
cell surface CD4 becomes dramatically down-regulated in
HHV-7?infected cells.[14] In contrast to many other herpesvirus,
the range of host cells which can be infected by HHV-7 is small.
Apart from CD4+ T cells, macrophages have been identified as
target cells in vivo and in vitro.[15,16] Moreover, simultaneous replication
of HHV-7 and HHV-6B was found in CD68+ positive
cells of monocytic lineage in Kaposi?s sarcoma.[16] Infectious virus
can be isolated from the saliva of up to 75% of healthy individuals,[
17,18] but is only rarely found in breast milk.[19] Therefore,
saliva is considered as the main route of transmission.[20] Worldwide,
high seroprevalence rates have been reported (for a review
see Black & Pellett[1]). Primary infection mostly occurs within
the first 5 years of life, resulting in seroprevalence rates of 70 to
90% in young children and adolescents.[21,22] During primary infection,
HHV-7 DNA sequences can be detected in peripheral
blood mononuclear cells (PBMC) at acute and convalescent
stages. HHV-7 DNA is excreted into saliva and transiently into
stool at an early convalescent stage.[23]
After primary infection, HHV-7 is able to establish a latent
infection in PBMC, from which it can be reactivated.[24] In addition,
the presence of viral antigens indicative of viral replication
has been demonstrated in salivary glands and in a wide variety of
normal tissues, indicating chronic persistent HHV-7 infection.[
25,26] Although neutralizing antibodies and T cells specifically
targeting HHV-7 infected cells are generated,[11,27] little is
known about the immune response controlling HHV-7 infection.
The genetic similarities between HHV-7 and other members
of the ?-herpesvirus subfamily render the development of
HHV-7?specific diagnostic tools a challenging project. Unique
nucleotide sequences allow for HHV-7?specific detection by
polymerase chain reaction (PCR), Southern blot and in situ hybridization.
By PCR, HHV-7 DNA can be detected in up to 90%
of PBL of healthy adults.[28,29] The evaluation of various immunoassays
for detection of virus-specific serum antibodies indicated
that most human sera contain cross-reactive antibodies
against HHV-6 and HHV-7, and that the degree of cross-reactivity
varies between individual serum specimens.[30] Immunogenic
proteins of HHV-7 and HHV-7?infected cells have been identified.[
31] An 85-kDa phosphoprotein (pp85) represents an immunodominant
protein specific for HHV-7,[32] and is localized to
the tegument substructure of the HHV-7 virion.[33] In addition, a
89-kDa protein was identified as a HHV-7?specific serologic
marker by immunoblot assay.[34] Recombinant proteins have been
developed, which can be used for diagnostic purposes.[35] In most
studies, PCR is the method most often applied for the detection
of HHV-7. However, in particular in studies focusing on a pathogenic
association between HHV-7 and diseases, PCR-based data
have to be interpreted with caution, in respect to the latent and
chronic persistent infection of HHV-7 found in various host tissues.[
26]
2. Disease Association
HHV-7 is reactivated from latently infected PBL by T cell
activation, whereas HHV-6B can not be reactivated under similar
conditions. However, latent HHV-6B can be recovered after the
cells become infected with HHV-7.[24] Once reactivated, the
HHV-6B genomes become prominent and HHV-7 disappears.
The ability of HHV-7 to reactivate HHV-6B from latent infections
complicates interpretation of data which focus on the association
of HHV-7 with diseases and results in ongoing debate about the
pathogenic role of HHV-7 in the investigated disorders.
2.1 Primary Infection
Based on seroepidemiologic data, primary infection occurs
early in life. Exanthema subitum (or roseola infantum) is a common
childhood disease characterized by fever, rash and neurologic
complications in some patients. HHV-6B was originally
identified as the primary causative agent of exanthema subitum.[
36] Seroconversion and isolation of HHV-7 from PBMC in
children with exanthema subitum, but without evidence of prior
or concurrent HHV-6 infections, prove that primary infection
with HHV-7 can manifest as exanthema subitum.[2,4] However,
some patients had previous HHV-6?related exanthema subitum[
37] and a simultaneous rise in anti?HHV-6 antibodies. These
observations, and the fact that HHV-6 is usually acquired earlier
in life than HHV-7,[4] raise the possibility that HHV-7 infection
may contribute only indirectly to exanthema subitum by reactivation
of HHV-6 in some children.[38] Neurologic complications
of HHV-7?associated illness seem to be quite frequent. Seizures,
febrile convulsion and even hemiplegia have been reported in the
context of primary infection with HHV-7,[4,39] and encephalitislike
symptoms have occurred in a child after bone-marrow transplantation.[
40]
Primary infection of HHV-7 has also been attributed to cases
clinically manifesting as rubella and measles.[3] Moreover, macular
or maculopapular rashes, considered to be drug eruptions
resulting from antibiotics and mononucleosis-like disease, may
in fact be manifestations of primary infection with HHV-7 or
co-infections together with Epstein-Barr virus (EBV).[41,42] Thus,
HHV-7 should be considered as a cause in a variety of macularpapular
rashes in children.
310 Kempf
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2.2 HHV-7 and Pityriasis Rosea, Psoriasis and Other
Inflammatory Skin Diseases
Pityriasis rosea is an exanthematic, inflammatory, and spontaneously
resolving skin disease. There is substantial evidence for
an infectious etiology of pityriasis rosea and various infectious
agents, including viruses, have been proposed as causative agents
(for a review see Kempf and Burg[43]). In 1997, Drago et al.[44,45]
reported the detection of HHV-7 in all skin, plasma and PBMC
specimens from 12 patients with pityriasis rosea, by nested PCR.
Moreover, cytopathic effects were observed in SupT1 cells
(lymphoblastoid T cell line) after co-cultivation with the PBMC
of patients with pityriasis rosea, and herpesvirus-like particles
were found in the supernatants of co-cultures by electron microscopy.
The authors concluded that ?the finding of HHV-7 DNA in
plasma which reflects viral replication and virulence strongly
supports its causative role in pityriasis rosea?,[45] or an association,
not necessarily causative, between HHV-7 and the disease.[
44]
Subsequently, several other investigators analyzed the presence
of HHV-7 in patients with pityriasis rosea (see table I). Most
of these studies have been performed in Italy and Japan. Two
groups applied the same PCR protocol for detection of HHV-7 as
Drago et al.,[44,45] but HHV-7 DNA was completely absent or
found in only 16 of 36 (44%) plasma samples of patients with
pityriasis rosea.[46,47] Moreover, immunoglobulin M antibodies
against HHV-7 were not detected, and there was no increase in
immunoglobulin G titers (except for one case), although both
antibodies would have been expected to rise in primary and/or
reactivation infections.[46,48] Additionally, investigations of skin
biopsies of pityriasis rosea lesions mostly showed an absence, or
very low detection rate, of HHV-7 DNA.[49-51] In our study, we
focused on the presence of HHV-7 in skin biopsies of herald
patches and secondary pityriasis rosea lesions.[49] Two detection
methods, a nested PCR protocol[6] and an immunohistochemical
approach using a well-characterized monoclonal antibody directed
against the structural phosphoprotein pp85 of HHV-7,
were employed. HHV-7 was detected in only 1 of 13 (8%) archival
skin biopsies of pityriasis rosea lesions, which represented a
smaller incidence than in controls of normal skin [2 of 14 biopsies
(14%)].[49] In several studies, HHV-7 DNA was found in similar,
or even lower, percentages in the PBL or PBMC of patients with
pityriasis rosea compared with controls.[50,52-54] Two studies of
HHV-7 DNA in plasma, which serves as a marker of active infection,
demonstrated the absence of HHV-7,[54,55] whereas in one
study HHV-7 DNA was present in only 16 of 36 (44%) of plasma
samples.[46]
Controversial data might be partly because of geographic
variations in the prevalence of HHV-7 infections, as well as dif-
Table I. Viral studies on human herpesvirus 7 in pityriasis rosea
Reference Study country Investigated material Detection methods Results
Drago et al.[44,45] Italy Skin, PBMC, plasma PCR, EM, cell culture HHV-7 DNA in all 12 PR
specimens
Cytopathic effect in co-cultures; herpesvirus-like particles in
supernatant of co-cultures
Kempf et al.[49] Switzerland Skin PCR, IHC HHV-7 in 1/13 PR samples and 2/14 controls
Yoshida[47] Japan Peripheral blood DNA PCR HHV-7 DNA in all samples of 4 patients with PR and 3
controls
Yasukawa et al.[52] Japan PBMC PCR, cell culture, SA HHV-7 DNA in 1/14 samples
Watanabe et al.[46] Japan Plasma PCR, SA HHV-7 DNA in 16/36 (44%) plasma samples of patients with
PR,
but not in 31 control samples. No detection of IgM and no increase
in IgG titers of antibodies against HHV-7
Kosuge et al.[53] Japan Serum, PBL PCR HHV-7 DNA in 13/30 (43%) and 14/25 (56%) PBMC samples of
patients and controls, respectively
Rise in titers of anti?HHV-7 antibodies in 2/44 cases
Offidani et al.[50] Italy PBMC, skin scales,
saliva and urine
PCR HHV-7 DNA in saliva of 5/12 (42%) patients and 14/20 (70%)
controls. No detection of HHV-7 DNA in all other samples
Chuh and Peiris[55] China Plasma, PBL PCR, SA No HHV-7 DNA in plasma in all 3 patients; HHV-7 DNA
in PBL of
only 1/3 patients
Chuh et al.[54] China Plasma, PBL PCR, SA No HHV-7 DNA in plasma, but in PBL samples of 7/15
(47%)
patients with PR and 5/15 (33%) controls
Antibodies in serum of all 15 patients and 15 controls
Wong et al.[51] Taiwan Skin PCR, viral culture HHV-7 DNA or virions in none of the biopsies of 24
patients and 20
controls
EM = electron microscopy; HHV-7 = human herpesvirus 7; IgG = immunoglobulin G; IgM =
immunoglobulin M; IHC = immunohistochemistry; PBL = peripheral
blood lymphocytes; PBMC = peripheral blood mononuclear cells; PCR = polymerase chain reaction; PR
= pityriasis rosea; SA = serologic assays.
HHV-7 in Dermatology 311
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ferences in the sensitivity and specificity of the applied detection
methods. Moreover, to assess the role of HHV-7 in inflammatory
diseases, several compartments (skin, plasma and PBL) of the
affected individuals should be evaluated for the presence of HHV-
7 virions, antigens or nucleic acids. In summary, so far there are
no consistent data supporting an association of HHV-7 and pityriasis
rosea.
In a recent article, ?-herpesviruses (CMV, HHV-6 and HHV-
7) were investigated as possible causative antigens in psoriasis.
Skin biopsies from ten patients with chronic plaque psoriasis
were investigated by PCR for the presence of HHV-7 DNA, but
HHV-7 could not be detected in involved or uninvolved skin.
Although viruses or viral antigens may play a role in the pathogenesis
of psoriasis, none of the ?-herpesviruses seem to be
linked to this common skin disease.
Ongradi et al.[56] reported simultaneous infection of HHV-7
and parvovirus B19 in papular-purpuric gloves-and-socks syndrome,
but it cannot be excluded that HHV-7 was merely reactivated
during infection with parvovirus B19. Apart from these
diseases, no other inflammatory skin diseases have yet been examined
for the presence of HHV-7, and the clinical manifestations
of HHV-7 reactivation are still to be identified.
3. HHV-7 and Immunosuppression
Recently, HHV-7 has been identified as an emerging pathogen
in transplant recipients. HHV-6 and HHV-7 are considered to
induce immunosuppression by targeting lymphocytes, natural
killer cells and monocytes.[57] After kidney transplantation, HHV-
7 DNA was detected (by PCR) in PBMC in 39% of the patients,
whereas only 9% of healthy controls showed ?HHV-7 DNAemia?.[
58] In this study, so called ?CMV disease or post-transplant?
occurring viral disease? was associated with rising antibody titers
to HHV-7. Patients with detectable HHV-7 DNA in their plasma
had significantly higher plasma CMV loads.[59] Recently, Kidd et
al.,[60] in a prospective study by clinicopathologic analysis,
showed that in patients with rejection, the presence of HHV-7
DNA in peripheral blood samples was associated with more episodes
of rejection. Two studies revealed that there was a significant
increase in ?CMV disease? occurring in patients with CMV
and HHV-7 co-infection, compared with those with CMV infection
alone.[60,61] Therefore, HHV-7 may act as a possible cofactor
in the development of ?CMV disease? in renal transplant patients
and may potentially exacerbate graft rejection. In liver transplant
recipients, HHV-7 may be the cause of some episodes of hepatitis
and pyrexia.[62] In contrast, no correlation between HHV-7 and
acute graft-versus-host disease or delayed engraftment could be
observed in patients with allogenic bone marrow transplantation.[
63]
Since CD4 is also used as a cellular receptor by HIV, the
interactions between HHV-7 and HIV have been intensively studied.
Both viruses can reciprocally block infection of CD4+ lymphoid
cells, as well as in macrophages in vitro.[13,15] In vivo, HHV-
7 was more frequently found in the lymph nodes of patients with
AIDS, than in individuals who were HIV-seronegative.[64] Contradictory
data of the viral load of HHV-7 in the saliva of patients
infected with HIV have been reported and may result from fluctuations
of viral load in the saliva within the same individual over
time.[65,66] However, the data are controversial and further studies
are needed to clarify the in vivo interaction between HHV-7 and
HIV.
4. HHV-7 and Neoplasms
No transforming genes of HHV-7 have been identified, thus
rendering it rather implausible that HHV-7 is involved in the direct
tumorigenesis of neoplasms. However, since the cellular tropism
of HHV-7 is mainly restricted to cells of lymphoid origin,
the question arose whether lymphoid neoplasms are linked to this
lymphotropic herpesvirus. Hodgkin?s disease, which is considered
to be of viral origin, has been intensively examined for the
presence of HHV-7. Viral DNA was found by nested PCR in 33
of 88 (38%) Hodgkin?s disease biopsies, with seven of those cases
showing co-infection with HHV-6, and 11 cases containing EBV
DNA.[67] In another study, HHV-7 DNA was detected significantly
more often by PCR in Hodgkin?s disease biopsies independently
of the histological type, compared with reactive lymph
nodes.[68] However, quantitative PCR revealed only a low level
of viral load in the majority of the examined samples. Moreover,
in situ hybridization for HHV-7 DNA was positive in a low number
of small T lymphocytes, and consistently negative in Hodgkin
and Reed-Sternberg cells, which also appeared negative for HHV-
7 at immunohistochemistry.[68] In contrast to EBV, ?-
herpesviruses are therefore unlikely to have a role in the etiology
of Hodgkin?s disease. The presence of HHV-7 is most probably a
result of recruitment of nonmalignant, reactive T cells in Hodgkin?s
disease tissue.[68] In regard to non-Hodgkin?s lymphomas,
HHV-7 could not be found by Southern blot hybridization in 32
lymph node specimens with non-Hodgkin?s lymphomas.[69]
Evaluating primary cutaneous T and B cell lymphomas,
Nagore et al.[70] detected HHV-7 DNA in 9 of 64 (14%) samples
comprising mycosis fungoides, CD30+ large cell lymphoma, follicle
center cell lymphoma and one case of marginal zone lymphoma.[
70] We have previously analyzed 37 fresh, frozen and formalin-
fixed, paraffin-embedded biopsies of lymphomatoid
312 Kempf
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papulosis, which belongs to the spectrum of primary cutaneous
CD30+ T cell lymphomas, and found HHV-7 DNA sequences by
nested PCR in 5 of 37 (14%) biopsies.[71] Thus far, these data do
not indicate an association between HHV-7 and nodal or primary
cutaneous T or B cell lymphomas.
Human herpesvirus 8 (HHV-8) has been identified as a causative
factor in the pathogenesis of Kaposi?s sarcoma, a vascular
neoplasm occurring in various epidemiologic forms.[72,73] HHV-8
is a ?conditio sine qua non? for Kaposi?s sarcoma development,
but other cofactors are involved in the maintenance and propagation
of tumor growth. Studies on the presence of other viruses in
Kaposi?s sarcoma, including HHV-7, revealed controversial data
(for a review see Kempf & Adams[74]). We found HHV-7 DNA
and structural antigens (pp85) in 9 of 32 (28%) patients with
AIDS-associated Kaposi?s sarcoma and in 1 of 7 patients with
classical-sporadic HIV-negative Kaposi?s sarcoma,[16] whereas
HHV-7 could not be detected in non?AIDS-related Kaposi?s sarcoma
forms by others.[75] In some of the Kaposi?s sarcoma tumors,
co-infection of CD68+ cells of monocytic lineage with
HHV-6B and HHV-7 could be observed. HHV-7 infection has
been shown to cause significant immunomodulatory effects with
increased levels of cytokines (tumor necrosis factor-?, transforming
growth factor-? and interferon-?).[76] Thus, we hypothesize
that infection of tumor-infiltrating CD68+ cells by HHV-6 and
HHV-7 may contribute to tumor propagation via secretion of tumor
growth-enhancing cytokines.
5. HHV-7 and Antivirals
With increasing evidence of HHV-7 as a cofactor for ?viral
disease? in transplant recipients, it becomes more important to
analyze antivirals for their efficacy to inhibit HHV-7 replication.
HHV-7 lacks a homologue of the thymidine kinase gene. Therefore,
HHV-7 replication is largely unaffected by thymidine kinase?
dependent drugs, such as aciclovir and its derivatives.[10,77] There
are controversial data on the effect of ganciclovir on HHV-7 in
renal transplant recipients. Brennan et al.[78] reported that
ganciclovir, administered either orally or intravenously, had no
effect on the prevalence of HHV-7 viremia,[78] whereas antiviral
therapy with ganciclovir reduced the load of CMV, HHV-6 and
HHV-7 in another study.[79] Nucleoside phosphonates, including
cidofovir, and inhibitors of DNA polymerases, such as foscarnet
(phosphonoformic acid), are promising drugs against HHV-7,
since they are potent inhibitors of HHV-7 replication.[80]
6. Conclusion
Thirteen years after the discovery of HHV-7, there has been
considerable progress in characterizing its genetic structure and
the virus-induced effects on infected host cells, and in the development
of diagnostic tools. Nevertheless, the role of HHV-7 in
various systemic diseases, as well as in skin disorders, has still to
be defined. Well-characterized, standardized and widely available
diagnostic tools are an important prerequisite to enable comparison
of study results and to increase our knowledge on the
biology and pathogenesis of HHV-7. In regard to the fact that
human herpesviruses in general are often linked to skin disorders,
and that HHV-7 infection can manifest with a variety of maculopapular
rashes in childhood, it can be expected that additional
clinical manifestations of primary and reactivated HHV-7 infection
will be identified in the future. Moreover, the ability of HHV-
7 to induce cytokine production in infected cells could make
HHV-7 an important pathogenic cofactor in inflammatory conditions,
and also in neoplastic processes where the cytokine milieu
is of utmost importance for the regulation of tumor growth. In
addition, the relatively restricted cellular tropism of HHV-7 for
lymphocytes and macrophages may render this virus an interesting
vector for gene therapy. Thus, HHV-7 is likely to become an
emerging pathogen in dermatology, and in general.
Acknowledgments
The author declares no conflict of interest or financial support for the
preparation of this manuscript.
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Correspondence and offprints: Dr Werner Kempf, Department of Dermatology,
University Hospital, Gloriastrasse 31, Zurich, CH-8091, Switzerland.
E-mail: kempf@derm.unizh.ch
HHV-7 in Dermatology 315
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