Human herpesvirus 6 infection after living related liver transplantation

Human Herpesvirus 6B Greatly Increases Risk of Depression by Activating Hypothalamic-Pituitary -Adrenal Axis during Latent Phase of Infection

Little is known about the effect of latent-phase herpesviruses on their host. Human herpesvirus 6B (HHV-6B) is one of the most ubiquitous herpesviruses, and olfactory astrocytes are one of the most important sites of its latency. Here, we identified SITH-1, an HHV-6B latent protein specifically expressed in astrocytes. Mice induced to produce SITH-1 in their olfactory astrocytes exhibited olfactory bulb apoptosis, a hyper-activated hypothalamic-pituitary-adrenal (HPA) axis and depressive symptoms. The binding of SITH-1 to the host protein calcium-modulating ligand (CAML) to form an activated complex promoted the influx of extracellular calcium. The serum antibody titers for depressive patients with respect to this activated complex were significantly higher than for normal controls (p = 1.78 × 10⁻¹⁵), when the antibody positive rates were 79.8% and 24.4%, respectively, and the odds ratio was 12.2. These results suggest that, in the latent phase, HHV-6B may be involved in the onset of depression.

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We identified SITH-1, a new protein specific to HHV-6B latent infection

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Mice expressing SITH-1 at HHV-6B latent infection site had depressive symptoms

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Depressive symptoms due to SITH-1 were associated with a hyper-activated HPA axis

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SITH-1-specific antibody detection significantly greater in depressive patients

Primary infection with human herpes virus type 6, post-pediatric liver transplantation-A pathogen to remember

BACKGROUND

In recent years, liver transplantation (LT) has become a well-accepted therapeutic modality for children with end-stage liver disease, with transplantation surgery being performed at a younger age. Human herpes virus 6 (HHV-6) infection occurs in most children within the first 2 years of life, therefore, data on primary HHV-6 infection in pediatric liver transplant recipients is scarce.

OBJECTIVE

To describe the course of primary HHV-6 infection after pediatric LT.

METHODS

Medical files, between the years 2015-2016, of post-LT pediatric patients with suspected primary HHV-6 infection were reviewed. Clinical and laboratory data for enrolled cases were evaluated. Primary infection was defined as DNAemia in children who were seronegative prior to transplantation or seroconversion from negative to positive IgG posttransplantation.

RESULTS

Four cases of primary HHV-6 (type B) infection were identified among the 26 children who had undergone LT at our center during the study period. All patients were <1 year old and presented with fever, hepatitis, and elevated inflammatory markers, most (75%) within a short-period posttransplantation. All were initially treated with empiric antibiotics for a suspected bacterial infection and three underwent liver biopsy, one showing signs of rejection. Three were treated with antiviral therapy with a gradual resolution of symptoms.

DISCUSSION

Primary HHV-6 should be taken into account in young children shortly after LT, especially when presenting with fever and elevated liver enzymes. Treatment with antiviral therapy should be considered.

CONCLUSIONS

In young infants post-LT, a high index of suspicion may promote early detection of HHV-6 primary infection and prevent serious complications.

Clinical course of human herpesvirus 6 infection in pediatric living donor liver transplantation

Differentiation between active and latent viral infection is critical for analysis of HHV-6-associated disease. HHV-6 infection has been associated with several clinical manifestations; however, the precise role of HHV-6 in pediatric LDLT remains unclear. This retrospective cohort study included 33 pediatric patients who received LDLT. All of the recipients were monitored for HHV-6 infection using viral isolation and real-time PCR. HHV-6 infection was observed in 14 of 33 (42.4%) recipients, and HHV-6B infection occurred within 2 weeks after LDLT in 10 of 14 (71.4%) recipients. HHV-6 was isolated from 10 of 33 (30.3%) recipients. Multivariate analysis showed that independent predictors of HHV-6B infection were age (OR 0.975; 95% CI 0.943-0.999; P = .041), PELD (OR 1.091; P = .038), and biliary atresia (OR 16.48; P = .035). The occurrence of unexplained fever was significantly higher in recipients with HHV-6B infection (11/14) compared with uninfected recipients (6/19) (P = .013). Additionally, ALT levels at 8 and 9 weeks after transplantation were significantly higher in the recipients with HHV-6B infection. Younger age, high MELD/PELD score, and biliary atresia as an underlying disease were identified as risk factors for viral infection.

Reactivation of human herpesviruses 6 and 7 in Kawasaki disease

Objectives: Kawasaki disease (KD) is one of the most common childhood vasculitides. Some serological studies have suggested an etiological relationship between KD and human herpesvirus (HHV)-6 or HHV-7. However, primary or reactivated HHV-6 and -7 has not been fully investigated in patients with KD. Methods: Twenty-three patients with KD were prospectively enrolled in this study. Peripheral blood was collected in the acute and convalescence phases, and HHV-6 and -7 viral loads were measured by real-time PCR. Results: In the acute phase, HHV-6 and -7 DNA was detected in 7 (30%) patients each, compared to 13 (57%) and 9 (39%) patients in the convalescence phase, respectively. HHV-6 and -7 DNA loads were significantly higher in the convalescence phase than in the acute phase. Significant increases in HHV-6 and -7 DNA loads were not observed in disease control patients. Taking into account HHV-6 and -7 serostatus, reactivation of HHV-6 and -7 was observed in 7 and 9 patients, respectively. KD patients with HHV-6 reactivation showed higher C-reactive protein levels and more frequently required steroid therapies than patients without reactivation. Conclusion: HHV-6 and -7 reactivation is frequent in KD patients. HHV-6 reactivation might exacerbate the severity of KD.

Buffering agent via insulin-mediated activation of PI3K/AKT signaling pathway to regulate lipid metabolism in lactating goats

Ruminants are often fed a high-concentrate (HC) diet to meet lactating demands, yet long-term concentrate feeding induces subacute ruminal acidosis (SARA) and leads to a decrease in milk fat. Buffering agent could enhance the acid base buffer capacity and has been used to prevent ruminant rumen SARA and improve the content of milk fat. Therefore, we tested whether a buffering agent increases lipid anabolism in the livers of goats and influences of milk fat synthesis. Twelve Saanen-lactating goats were randomly assigned to two groups: one group received a HC diet (Concentrate: Forage=60:40, Control) and the other group received the same diet with a buffering agent added (10 g sodium butyrate, C(4)H(7)NaO(2); 10 g sodium bicarbonate, NaHCO(3); BG) over a 20-week experimental period. Overall, milk fat increase (4.25+/-0.08 vs. 3.24+/-0.10; P<0.05), and lipopolysaccharide levels in the jugular (1.82+/-0.14 vs. 3.76+/-0.33) and rumen fluid (23,340+/-134 vs. 42,550+/-136) decreased in the buffering agent group (P<0.05). Liver consumption and release of nonesterified fatty acid (NEFA) into the bloodstream increased (P<0.05). Phosphatidylinositol 3-kinase (PI3K), protein kinase B (AKT) and ribosomal protein S6 kinase (p70S6K) up-regulated significantly in the livers of the buffering agent group (P<0.05). It also up-regulated expression of the transcription factor sterol regulatory element binding protein-1c (SREBP-1c) and its downstream targets involved in fatty acid synthetic, including fatty acid synthetase (FAS), stearoyl-CoA desaturase (SCD-1) and acetyl-CoA carboxylase 1 (ACC1) (P<0.05). The BG diet increased insulin levels in blood (19.43+/-0.18 vs. 13.81+/-0.10, P<0.05), and insulin receptor was likewise elevated in the liver (P<0.05). Cumulatively, the BG diet increased plasma concentrations of NEFA by INS-PI3K/AKTSREBP-1c signaling pathway promoting their synthesis in the liver. The increased NEFA concentration in the blood during BG feeding may explain the up-regulated in the milk fat of lactating goats.

HHV-6 in liver transplantation: A literature review

Human herpesvirus 6 (HHV-6A and HHV-6B) can cause primary infection or reactivate from latency in liver transplant recipients, which can result in a variety of clinical syndromes, including fever, hepatitis, encephalitis and higher rates of graft dysfunction as well as indirect effects including increased risks of mortality, CMV disease, hepatitis C progression and greater fibrosis scores. Although HHV-6 infection is currently diagnosed by quantifying viral DNA in plasma or blood, biopsy to demonstrate histopathological effects of HHV-6 remains the gold standard for diagnosis of end-organ disease. HHV-6 reactivation may be restricted to the infected organ with no evidence of active infection in the blood. HHV-6 infections in liver transplant patients are mostly asymptomatic, but clinically significant tissue-invasive infections have been treated successfully with ganciclovir, foscarnet or cidofovir. Inherited chromosomally integrated HHV-6 (ciHHV-6), in either the recipient or the donor organ, may create confusion about systemic HHV-6 infection. Recipients with inherited ciHHV-6 may have an increased risk of opportunistic infection and graft rejection. This article reviews the current scientific data on the clinical effects, risk factors, pathogenesis, diagnosis and treatment of HHV-6 infections in liver transplant recipients.

Human herpesvirus-6 and polyomaviruses DNAemia in children and young adult patients after kidney transplantation

Aims: Human herpesvirus-6 (HHV-6) and polyomaviruses (HPyV) establish latency and reactivate in immunocompromised hosts. The prevalence of their infections was investigated in pediatric and young adult kidney transplant recipients. Materials & methods: Blood was obtained from 83 patients. Quantitative real-time polymerase chain reactions were conducted to quantify HHV-6 and HPyV loads; nested PCR and reverse transcriptase-PCR assays were conducted to differentiate HHV-6A from 6B and to evaluate the presence of transcripts. Results: HHV-6 and HPyV DNAemia were detected in 19.3 and 18.1% patients, respectively. No association between HHV-6 and HPyV DNA presence, age of patients and time from transplant was observed. Conclusion: HHV-6 infection in immunosuppression setting was as common as those of HPyVs that are commonly recognized as opportunistic agents.

Coinfection of human herpesviruses 6A (HHV-6A) and HHV-6B as demonstrated by novel digital droplet PCR assay

The human herpesviruses HHV-6A and HHV-6B have been associated with various neurologic disorders partly due to the detection of elevated viral DNA levels in patients compared to controls. However the reported frequency of these viruses varies widely, likely reflecting differences in PCR methodologies used for detection. Digital droplet PCR (ddPCR) is a third generation PCR technology that enables the absolute quantification of target DNA molecules. Mounting evidence of the biological differences between HHV-6A and HHV-6B has led to their recent reclassification as separate species. As it is now especially relevant to investigate each virus, our objectives were to first design a multiplex HHV-6A and HHV-6B ddPCR assay and then to investigate the incidence of HHV-6A and HHV-6B coinfection in samples from healthy donors and patients with MS, a disease in which HHV-6 is thought to play a role. In our assessment of healthy donors, we observed a heretofore-underappreciated high frequency of coinfection in PBMC and serum, and found that our assay precisely detects both HHV-6A and HHV-6B chromosomally integrated virus, which has important implications in clinical settings. Interestingly, upon comparing the saliva from MS patients and healthy donors, we detected a significantly elevated frequency of coinfection in MS saliva; increased detection of HHV-6A in MS patients is consistent with other studies suggesting that this viral species (thought to be more neurotropic than HHV-6B) is more prevalent among MS patients compared to healthy donors. As the biology and disease associations between these two viral species differ, identifying and quantifying both species of HHV-6 may provide clinically relevant information, as well as enhance our understanding of the roles of each in health and disease.

Acute hepatitis with periportal confluent necrosis associated with human herpesvirus 6 infection in liver transplant patients

OBJECTIVES

To correlate human herpesvirus 6 (HHV-6) viral load with pathologic features in graft acute hepatitis of unknown origin.

METHODS

Liver frozen samples from 26 patients with graft hepatitis of unknown origin were available for HHV-6 DNA quantification.

RESULTS

In 10 (38.5%) of 26 liver samples, HHV-6 DNA was detectable, with a median viral load of 3.84 log10 copies/10⁶ cells. Confluent periportal necrosis was observed in 4 of 10 patients and associated with high viral load. These 4 patients responded to antiviral therapy. Mild unspecific hepatitis was observed in 4 patients with low intragraft viral load and in 2 patients with high viral load in a context of deep immunosuppression. Patients with HHV-6-negative graft hepatitis disclosed lobular necrotico-inflammatory activity without periportal necrosis.

CONCLUSIONS

Our study provides data supporting the pathogenic role of HHV-6 for liver allografts. The presence of confluent periportal necrosis could be a clue for prompt diagnosis of HHV-6-induced graft hepatitis.

Monitoring for HHV-6 infection after renal transplantation: evaluation of risk factors for sustained viral replication

BACKGROUND

Human herpesvirus-6 (HHV-6) is known to reactivate after renal transplantation and has been associated with several clinical manifestations. Risk factors for sustained viral replication, however, remain unclear.

METHODS

Thirty consecutive kidney transplant patients were prospectively followed for HHV-6 replication between February 2007 and February 2008. Plasma samples for DNA detection were collected from the donor and the recipient before transplantation and from the recipient weekly for the first 2 months after transplantation and then every 2 weeks for 2 additional months. HHV-6 active infection was defined as detection of viral DNA in plasma, by polymerase chain reaction, in at least two consecutive samples over an interval of at least 1 week.

RESULTS

Active viral infection was detected in 25% of the recipients before transplantation and 27% (8 of 30) of the patients after transplantation. The mean time to onset of viral replication was 28.1 days after transplantation and 7 of 8 (87.5%) were asymptomatic. Risk factors associated with active HHV-6 infection were receiving an organ from a living donor (P=0.028), recipients with IgM antibodies detected before transplantation (P=0.005), and pretransplantation recipient HHV-6 viral load more than 10,000 copies/mL plasma (P=0.034).

CONCLUSIONS

Active HHV-6 infection occurs early after renal transplantation and is mostly asymptomatic. Donor or recipient infection may occur at the time of transplantation and are related to higher rates of posttransplantation infections.

Novel marmoset (Callithrix jacchus) model of human Herpesvirus 6A and 6B infections: immunologic, virologic and radiologic characterization

Human Herpesvirus 6 (HHV-6) is a ubiquitous virus with an estimated seroprevalence of 95% in the adult population. HHV-6 is associated with several neurologic disorders, including multiple sclerosis, an inflammatory demyelinating disease affecting the CNS. Animal models of HHV-6 infection would help clarify its role in human disease but have been slow to develop because rodents lack CD46, the receptor for cellular entry. Therefore, we investigated the effects of HHV-6 infections in a non-human primate, the common marmoset Callithrix jacchus. We inoculated a total of 12 marmosets with HHV-6A and HHV-6B intravenously and HHV-6A intranasally. Animals were monitored for 25 weeks post-inoculation clinically, immunologically and by MRI. Marmosets inoculated with HHV-6A intravenously exhibited neurologic symptoms and generated virus-specific antibody responses, while those inoculated intravenously with HHV-6B were asymptomatic and generated comparatively lower antibody responses. Viral DNA was detected at a low frequency in paraffin-embedded CNS tissue of a subset of marmosets inoculated with HHV-6A and HHV-6B intravenously. When different routes of HHV-6A inoculation were compared, intravenous inoculation resulted in virus-specific antibody responses and infrequent detection of viral DNA in the periphery, while intranasal inoculation resulted in negligible virus-specific antibody responses and frequent detection of viral DNA in the periphery. Moreover, marmosets inoculated with HHV-6A intravenously exhibited neurologic symptoms, while marmosets inoculated with HHV-6A intranasally were asymptomatic. We demonstrate that a marmoset model of HHV-6 infection can serve to further define the contribution of this ubiquitous virus to human neurologic disorders.

Human herpesvirus 6 (HHV-6) disease in the setting of transplantation

PURPOSE OF REVIEW

Human herpesvirus 6 (HHV-6) frequently reactivates after solid-organ and hematopoietic cell transplantation (HCT), and it has been associated with important outcomes in these settings. In 1-2% of recipients or donors, HHV-6 was inherited through chromosomal integration. Although HHV-6 chromosomal integration has not been associated with disease, the resulting very high levels of HHV-6 DNA in human tissue and blood samples can be challenging to interpret in the transplant setting. This review addresses the recent findings regarding the clinical outcomes associated with HHV-6 as well as diagnostic and therapeutic concerns.

RECENT FINDINGS

The evidence supports a causal association between HHV-6 and central nervous system disease. New studies have further characterized the impact of HHV-6 on the central nervous system. In addition, new studies have explored the associations between HHV-6 and other important outcomes. The implications of integrated HHV-6 in transplant recipients remain undefined, though the possibility of an association with organ rejection has been suggested. New exploratory data exist regarding the safety of antiviral prophylactic and preemptive strategies.

SUMMARY

Our understanding of the full clinical impact of HHV-6 in the transplant population remains incomplete. A large antiviral trial would not only help to further define causality between HHV-6 associated clinical outcomes but also start to define preventive strategies.

Human herpesvirus-6 infections in kidney, liver, lung, and heart transplantation: review

Human herpesvirus-6 (HHV-6), which comprises of HHV-6A and HHV-6B, is a common infection after solid organ transplantation. The rate of HHV-6 reactivation is high, although clinical disease is not common. Only 1% of transplant recipients will develop clinical illness associated with HHV-6 infection, and most are ascribable to HHV-6B. Fever, myelosuppression, and end-organ disease, including hepatitis and encephalitis, have been reported. HHV-6 has also been associated with various indirect effects, including a higher rate of CMV disease, acute and chronic graft rejection, and opportunistic infection such as invasive fungal disease. All-cause mortality is increased in solid organ transplant recipients with HHV-6 infection. HHV-6 is somewhat unique among human viruses because of its ability to integrate into the host chromosome. The clinical significance of chromosomally integrated HHV-6 is not yet defined, although a higher rate of bacterial infection and allograft rejection has been suggested. The diagnosis of HHV-6 is now commonly made using nucleic acid testing for HHV-6 DNA in clinical samples, but this can be difficult to interpret owing to the common nature of asymptomatic viral reactivation. Treatment of HHV-6 is indicated in established end-organ disease such as encephalitis. Foscarnet, ganciclovir, and cidofovir have been used for treatment.

Human herpesvirus 6B induces phenotypic maturation without IL-10 and IL-12p70 production in dendritic cells

Human herpesvirus 6B (HHV-6B) is the causative agent of the common childhood febrile illness, exanthema subitum. The virus is predominantly regarded as a T-cell tropic virus, although in reality it has the ability to infect a wide variety of cell types including monocytes, macrophages and dendritic cells (DC). Although DC are important immune regulators, the modulating effects of HHV-6B on DC are controversial. Here, we examine the phenotypic and functional consequences of HHV-6B infection of DC. The addition of HHV-6B to immature DC led to expression of the nuclear viral p41 protein and cell surface expression of the viral glycoprotein gp60/110 consistent with HHV-6B infection. Nevertheless, HHV-6B did not induce noticeable cytopathogenic effects or cell death in infected DC. Importantly, HHV-6B infection induced a partial phenotypic maturation of immature DC as demonstrated by a substantial increase in the expression of HLA-DR, CD86 and CD40, whereas only a minor increase in CD80 and CD83 was observed. This phenotypic maturation was, however, not followed by functional maturation, because HHV-6B infection did not induce IL-10 and IL-12p70 production in immature DC. However, infected DC were still able to react to bacteria-derived stimuli such as lipopolysaccaharide by an even more pronounced production of IL-10 and IL-12p70 when compared to that of uninfected DC.

A report of human herpesvirus 6-associated encephalitis in a solid organ transplant recipient and a review of previously published cases

Human herpesvirus 6 (HHV-6) is a common pathogen among children, classically presenting as fever and rash that resolve without specific therapy (exanthem subitum or roseola infantum). Also identified as a pathogen in hematopoietic cell transplant and solid organ transplant (SOT) recipients, it has been recognized as a cause of limbic encephalitis, characterized by confusion and amnesia, with magnetic resonance imaging findings of T2 hyperintensity of the amygdala and hippocampus. We report a case of limbic encephalitis associated with HHV-6 infection in a liver transplant recipient, and we review previously reported cases of HHV-6 encephalitis in SOT recipients.

Human herpesvirus-6 infections and infection-preventative measures in transplant recipients

Like the other herpesviruses, human herpesvirus (HHV)-6 is capable of persisting in the host after primary infection and can reactivate under immunosuppressed conditions. In stem cell transplantation recipients, HHV-6 reactivation is observed in 40–50% of patients and is linked to various clinical manifestations, including rash, delayed platelet engraftment and encephalopathy. HHV-6 reactivation is also relatively common in solid organ transplantation recipients, and is associated with graft dysfunction and subsequent development of human cytomegalovirus disease. In particular, HHV-6 has been recognized as a life-threatening pathogen for the development of encephalopathy after stem cell transplantation. Ganciclovir, foscarnet and cidofovir are effective against HHV-6 in vitro. However, success rates are not high for patients who have developed encephalopathy. Plasma HHV-6 DNA-guided pre-emptive approaches have not been successful owing to the dynamic kinetics of HHV-6 reactivation. Establishment of optimal strategies is needed to prevent HHV-6-associated complications, in particular encephalopathy.

Case report: human herpesvirus 6 reactivation associated with colitis in a lung transplant recipient

Whereas human herpesvirus 6 (HHV-6) reactivation is frequent in solid organ transplant recipients, symptomatic disease is rare. A case of colitis associated with HHV-6B reactivation was observed in a lung transplant recipient. This case report suggests that symptomatic HHV-6 infection may occur in the absence of detectable viremia.

Human herpesvirus 6 infection in adult living related liver transplant recipients

To analyze human herpesvirus 6 (HHV-6) infection in adult living related liver transplantation, we performed a virological analysis, including viral isolation, serological assay, and real-time polymerase chain reaction, of serially collected blood samples from 67 recipients. In addition, cytokine levels were measured to determine their role in viral reactivation. HHV-6 was isolated from only 4 recipients (6.0%), and viral DNA was detected in 15 (22.4%) of the 67 recipients. A significant increase in HHV-6 immunoglobulin G antibody titers was observed in 19 (28.4%) of the 67 recipients. Finally, 26 recipients (38.8%) had HHV-6 reactivation 2-6 weeks after transplantation. HHV-6 associated clinical features were analyzed in the 17 recipients presenting with either viremia or DNAemia. Two recipients with viremia and 3 recipients with DNAemia had unexplained fever at the time of viral infection. An increase in aminotransferase levels was observed in 2 recipients with viremia and 3 recipients with DNAemia. Recipients with liver cirrhosis caused by hepatitis B virus or hepatitis C virus infection as the underlying disease were more likely to have HHV-6 infection (P = 0.025). Mortality at the last follow-up in recipients with HHV-6 reactivation was significantly higher than in those without viral reactivation (P = 0.0118). Plasma interleukin-6 levels were significantly higher in the recipients with HHV-6 viremia than in the recipients without viremia at 4 weeks post-transplant (P = 0.0411). Moreover, tumor necrosis factor alpha levels were also higher in recipients with HHV-6 viremia (P < 0.0001) or reactivation (P = 0.0011) than in recipients without viremia or reactivation 4 weeks post-transplant.

Human herpesvirus 6 (HHV-6)-associated pleurisy after unrelated cord blood transplantation in children with chemotherapy-resistant malignant Lymphoma

Two children, 5 and 10 years of age, received unrelated cord blood transplantation (CBT) for malignant lymphoma. Both of them suffered from pleurisy with and without interstitial pneumonitis after transplantation. By the quantitative real-time polymerase chain reaction, human herpesvirus 6 (HHV-6) variant B DNA was detected in pleural effusion. This is the first report of HHV-6-associated pleurisy after hematopoietic stem cell transplantation. HHV-6-associated pleurisy should be considered as a complication after hematopoietic stem cell transplantation even in the absence of pneumonitis. Quantitative polymerase chain reaction is a useful tool for rapid detection of viral DNA, which may facilitate precise diagnosis and appropriate treatment.

Human herpesvirus 6 and central nervous system disease in hematopoietic cell transplantation

Human herpesvirus 6 infects virtually all children within the first few years of life and like other herpesviruses, establishes latency after primary infection. In immunocompromised hosts, especially hematopoietic cell transplant (HCT) recipients, HHV-6 has been demonstrated to reactivate frequently. This reactivation has been associated with a number of different clinical endpoints in HCT recipients, including central nervous system (CNS) disease. There have been many detailed descriptions of individual patients with HHV-6-associated encephalitis. In addition, longitudinal observational studies have established a correlation between systemic HHV-6 reactivation and CNS dysfunction. Further research is needed to define optimal diagnostic, prevention, and treatment strategies.

Human herpesvirus-6A and -6B encode viral immunoevasins that downregulate class I MHC molecules

Like all other members of the herpesvirus family, the closely related human herpesviruses-6 and -7 (HHV-6,7) persist in their host throughout life. In so doing, without exception, every member of the herpesvirus family has evolved mechanisms to avoid detection by the immune system. In particular, human cytomegalovirus (HCMV), mouse cytomegalovirus (MCMV), human herpesvirus-8 (HHV-8), and herpes simplex virus (HSV) all encode multiple proteins that interfere with proper MHC class I antigen presentation. The mechanisms employed by these viruses to effect removal of MHC class I from the cell surface vary. The U21 open reading frame from HHV-7 diverts class I MHC molecules to an endolysosomal compartment using an as-yet unknown mechanism. The two variants of HHV-6, HHV-6A and -6B, both possess a U21 open reading frame which contain only approximately 30% amino acid identity to the U21 sequence from HHV-7. Here we describe the characterization of the U21 gene products from HHV-6A and HHV-6B. Like HHV-7 U21, both of the HHV-6 U21 molecules bind to and divert class I MHC molecules to an endolysosomal compartment, effectively removing them from the cell surface, and providing a possible means of escape from immune detection.

Human herpesvirus-6 infection in solid organ and stem cell transplant recipients

HHV-6 has in recent years become recognized as a potential significant pathogen in both solid organ and stem cell transplant recipients. HHV-6 infections are common after transplantation regardless of the utilized diagnostic technique. Several different clinical manifestations have been described including fever, bone marrow suppression, encephalitis, skin rash, and hepatitis. The most important end-organ disease is encephalitis in stem cell transplant recipients that has been reported to have a mortality of at least 40%. HHV-6 is also considered an immunomodulatory and immunosuppressive virus that may facilitate super-infections with other opportunistic pathogens such as CMV and fungal infections and thereby contribute to overall mortality. No established therapy exists but both ganciclovir and foscarnet have been reported to have in vitro and in vivo efficacy against HHV-6.

Update on human herpesvirus 6 biology, clinical features, and therapy

Human herpesvirus 6 (HHV-6) is a betaherpesvirus that is closely related to human cytomegalovirus. It was discovered in 1986, and HHV-6 literature has expanded considerably in the past 10 years. We here present an up-to-date and complete overview of the recent developments concerning HHV-6 biological features, clinical associations, and therapeutic approaches. HHV-6 gene expression regulation and gene products have been systematically characterized, and the multiple interactions between HHV-6 and the host immune system have been explored. Moreover, the discovery of the cellular receptor for HHV-6, CD46, has shed a new light on HHV-6 cell tropism. Furthermore, the in vitro interactions between HHV-6 and other viruses, particularly human immunodeficiency virus, and their relevance for the in vivo situation are discussed, as well as the transactivating capacities of several HHV-6 proteins. The insight into the clinical spectrum of HHV-6 is still evolving and, apart from being recognized as a major pathogen in transplant recipients (as exemplified by the rising number of prospective clinical studies), its role in central nervous system disease has become increasingly apparent. Finally, we present an overview of therapeutic options for HHV-6 therapy (including modes of action and resistance mechanisms).

Detection of human herpesvirus 7 DNA by loop-mediated isothermal amplification

The reliability of loop-mediated isothermal amplification (LAMP), initially developed for the detection of human herpesvirus 7 (HHV-7), was evaluated in this study. Although a LAMP product was detected in HHV-7 DNA, neither HHV-6 nor human cytomegalovirus DNA produced a product. When agarose gel electrophoresis was used for the detection of LAMP products, the sensitivity of a 30-min HHV-7 LAMP reaction reached 250 copies/tube. The use of turbidity for the detection of the LAMP products gave a sensitivity of 500 and 250 copies/tube for 30- and 60-min reactions, respectively. Following these initial validation studies, clinical samples collected from two patients with primary HHV-7 infections were examined by HHV-7 LAMP. By use of agarose gel electrophoresis, HHV-7 LAMP products could be detected in acute-phase plasma samples but no LAMP product was detectable in convalescent-phase plasma samples from either patient. Since a turbidity assay is less sensitive than agarose gel electrophoresis, no HHV-7 LAMP product could be detected in plasma samples after a 30-min LAMP reaction. After a 60-min LAMP reaction, HHV-7 LAMP product could be detected in acute-phase plasma samples.

Rapid diagnosis of human herpesvirus 6 infection by a novel DNA amplification method, loop-mediated isothermal amplification

A novel nucleic acid amplification method, termed loop-mediated isothermal amplification (LAMP), which amplifies DNA with high specificity, efficiency, and rapidity under isothermal conditions, may be a valuable tool for the rapid detection of infectious agents. LAMP was developed for human herpesvirus 6 (HHV-6), and its reliability was evaluated in this study. Although LAMP products were detected in HHV-6 B and HHV-6 A DNA, they were not detected in HHV-7 and human cytomegalovirus DNA. The sensitivity of the original HHV-6 LAMP protocol was 50 copies/tube. In order to increase the method's sensitivity, HHV-6 LAMP was modified by increasing the primer concentration. As a result of the modification, sensitivity increased to 25 copies/tube. After these initial validation studies, 13 patients with fever were tested for HHV-6 by viral isolation, serological analysis, and HHV-6 LAMP. In three of the eight patients with primary HHV-6 infection, HHV-6 DNA was detected in whole blood by the original HHV-6 LAMP protocol in not only the acute phase but also the convalescent phase. HHV-6 DNA was detected by modified HHV-6 LAMP in all eight plasma samples collected in the acute phase; however, no HHV-6 DNA was detected in plasma samples collected in the convalescent phase. Although HHV-6 DNA was detected in both the acute and convalescent phases of whole-blood samples in patients with past HHV-6 infection, it was not detected in plasma samples that did not contain latent viral DNA. Thus, detection of HHV-6 DNA in plasma by using this modified HHV-6 LAMP protocol is appropriate for diagnosis of active HHV-6 infection.

In vitro and in vivo analysis of human herpesvirus-6 U90 protein expression

In order to establish a reliable method for the detection of human herpesvirus-6 (HHV-6) B antigens in peripheral blood mononuclear cells (PBMCs) collected from HHV-6 infected patients, we created a polyclonal antibody against the HHV-6 B U90 protein (IEA/ex3) and used it to examine the expression of this protein in virus-infected cells and patients' PBMCs. This antibody reacted with 170 and 195 kDa proteins in HHV-6 B-infected cord blood mononuclear cells. The IEA/ex3 antigen was detected in cord blood mononuclear cells at 6 hr post-infection, and the number of infected cells reached its maximum at 48 hr post-infection. The antigen stained in a punctate pattern and partially localized to the promyelocytic leukemia (PML) protein body. We also examined 60 PBMC samples from 60 febrile children (3-19 months old) and detected IEA/ex3 antigen in the PBMCs by laser-scanning microscopy. HHV-6 was isolated from 31 of the 60 samples. The sensitivity and specificity of the antigen detection were 84% (26/31) and 97% (28/29), respectively, in the samples with virus detected. The mean number of antigen-positive PBMCs was 409/10(6) cells in 20 samples with viral isolation. A significant correlation (r = 0.566; P = 0.008) was observed between the viral load and number of antigen-positive cells. Although IEA/ex3 antigen was detected by laser-scanning microscopy in PBMCs (without cultivation) collected from six patients with isolated virus, it was detected in only one sample by conventional fluorescence microscopy. Increasing the intensity by cultivation (24 hr) resulted in a higher detection rate (5/6) even by conventional fluorescence microscopy, which is available in most hospital laboratories.

Human herpesvirus-6 and -7 infections in transplantation

Human herpesvirus-6 (HHV-6) and human herpesvirus-7 (HHV-7) are ubiquitous in the human population and cause exanthem subitum, a benign disease seen in infancy. The viruses remain latent in the body after primary infection, and reactivate in immunocompromised patients. HHV-6 infection occurs in nearly 50% of all bone marrow and in 20-30% of solid-organ transplant recipients, 2-3 weeks following the procedure. It has been suggested that the viral infection and activation result in clinical symptoms, including fever, skin rash, pneumonia, bone marrow suppression, encephalitis, and rejection. In order to understand the viral infection in greater detail, several studies investigating the route of viral transmission and diagnostic procedures have been carried out. In contrast to studies of HHV-6 infection in organ-transplant recipients, the number of studies examining HHV-7 infection in these patients is limited. According to several recent studies, HHV-7 may act as a cofactor for cytomegalovirus disease in organ-transplant recipients.

Monitoring of active HHV-6 infection in bone marrow transplant recipients by real time PCR; comparison to detection of viral DNA in plasma by qualitative PCR

Twelve (46%) of the 26 patients had human herpesvirus 6 (HHV-6) viremia after bone marrow transplant (BMT). All isolates were recovered from the samples obtained at 2 weeks after BMT. The sensitivity and the specificity of detection of viral DNA in plasma by qualitative polymerase chain reaction (PCR) for monitoring active virus replication were 92% and 97% respectively. Moreover, the positive (85%) and negative (99%) predictive values were also high. The patients with HHV-6 viremia showed a clear peak in HHV-6 DNA in peripheral blood mononuclear cells (PBMCs) at 2 weeks after BMT, which was measured by real time PCR. The virus DNA level in PBMCs between the two groups (patients with viremia and patients without viremia) was statistically different at 2 weeks after BMT (P = 0.033). In patients with HHV-6 viremia, mean HHV-6 DNA copy number was higher in the samples collected at 2 weeks after BMT than the samples collected at any other time period.

Human herpesvirus 6 and human herpesvirus 7: emerging pathogens in transplant patients

Human herpesvirus 6 (HHV-6) and HHV-7 are two recently identified beta-herpesviruses, genetically related to human cytomegalovirus (CMV). Infection with both viruses is common worldwide with rates of seropositivity in adults over 90%. Infection with both viruses usually occurs in early childhood. In this age group HHV-6 is a cause of febrile illness including exanthem subitum, and likewise, primary HHV-7 infection has been associated with febrile illness. Similar to the other human herpesviruses, in particular CMV, the viruses have the potential for enhanced pathogenicity in the immunocompromised host. Active infection with both viruses is common following bone marrow or solid organ transplantation, most likely through reactivation of recipient's virus or re-infection considering their high prevalence in the population. Both viruses can be detected by PCR in the peripheral blood of healthy individuals and although the significance of blood-borne transmission is not clear, a preliminary study suggested that it was not significant for HHV-6. However, there is growing evidence that these viruses may be medically important in the post-transplant period. In bone marrow transplant patients HHV-6 has been associated with a range of clinical disease including encephalitis, interstitial pneumonitis, early and late graft failure and bone marrow suppression. There is also growing evidence for potential interactions among the beta-herpesviruses in liver and renal transplant patients. HHV-6 infection has been associated with an increased risk of developing CMV disease and opportunistic infections and HHV-7 infection has also been linked to an increased risk of CMV disease.

Viral infections and pediatric liver transplantation

Viral infections remain an important cause of morbidity and mortality following LTx in children. Increasing experience with both 'donor-associated' and 'community-acquired' viruses is leading to improved outcomes and the development of effective preventive strategies. The potential importance of emerging viral pathogens is an area of active research, which hopefully will also lead to effective treatments and potential preventive strategies for these newly recognized pathogens.

Sequential measurement of human herpesvirus 6 DNA with polymerase chain reaction method in pediatric living-related liver transplantation

BACKGROUND

Human herpesvirus 6 (HHV-6), a causative virus of exanthem subitum, may occasionally present with a severe clinical form in immunosuppressed patients after transplantation. In this study, HHV-6 DNA was sequentially measured with a polymerase chain reaction (PCR) method, a quick and sensitive modality in pediatric living-related liver transplantation (LTx).

METHODS

Subjects consisted of 5 post-operative biliary atresia patients undergoing living-related LTx at ages from 8 months to 4 yr. Immunosuppression was performed with Tacrolimus (blood trough level 8-18 within 1 month and 5-10 ng/mL thereafter) and low-dose steroid. Specimens were peripheral blood mononuclear cells (PBMC), plasma, and liver biopsy tissue. The amount of HHV-6 DNA was semiquantified as follows: 1+, 1-10; 2+, 10-100; 3+, 100-1000; 4+, over 1000 copies/105 PBMCs.

RESULTS

A total of 69 blood samples and three liver biopsies were provided for the examination. HHV-6 DNA in PBMC was positive in 2 donors and 3 recipients before LTx. Two patients with negative DNA were converted to 3+ at 2-3 wk after LTx and 3 with positive DNA remained 2+ to 3+ throughout the post-LTx period. Only 1 patient developed clinical symptoms, such as fever, liver dysfunction, petechiae, idiopathic thrombocytopenic purpura, and finally bone marrow suppression. HHV-6 DNA in the liver biopsy tissue and plasma in this patient were 4+ and 2+, respectively.

CONCLUSION

HHV-6 DNA in PBMC measured by the PCR method may be persistently high in pediatric recipients after living-related LTx. Although HHV-6 DNA in PBMC may be positive in case of evident infection, positivity in PBMC may not be always associated with the clinical symptoms.

Primary human herpesvirus 6 infection in liver transplant recipients

We detected primary human herpesvirus 6 (HHV-6) infection in 5 infants who received living related liver transplantation from their HHV-6 seropositive mothers. Primary HHV-6 infection was confirmed by demonstrating the seroconversion of HHV-6 antibodies with an immunofluorescence assay, by the isolation of the virus, or both. Seroconversion of HHV-6 immunoglobulin G antibody was demonstrated in all 5 recipients. HHV-6 was isolated from 3 of the 5 recipients between 2 and 3 weeks after transplantation. Moreover, the virus genome was detected in plasma by polymerase chain reaction in 4 of the 5 recipients during the same period. Although the 5 recipients had pyrexia at the time of primary HHV-6 infection, none of the recipients had a skin rash after defervescence. Clinical symptoms disappeared without specific antiviral treatment in all but 1 of the recipients.