Fall in human herpesvirus 6 seropositivity with age

From Viral Infection to Autoimmune Reaction: Exploring the Link between Human Herpesvirus 6 and Autoimmune Diseases

The complexity of autoimmunity initiation has been the subject of many studies. Both genetic and environmental factors are essential in autoimmunity development. Among others, environmental factors include infectious agents. HHV-6 is a ubiquitous human pathogen with a high global prevalence. It has several properties suggestive of its contribution to autoimmunity development. HHV-6 has a broad cell tropism, the ability to establish latency with subsequent reactivation and persistence, and a range of immunomodulation capabilities. Studies have implicated HHV-6 in a plethora of autoimmune diseases-endocrine, neurological, connective tissue, and others-with some studies even proposing possible autoimmunity induction mechanisms. HHV-6 can be frequently found in autoimmunity-affected tissues and lesions; it has been found to infect autoimmune-pathology-relevant cells and influence immune responses and signaling. This review highlights some of the most well-known autoimmune conditions to which HHV-6 has been linked, like multiple sclerosis and autoimmune thyroiditis, and summarizes the data on HHV-6 involvement in autoimmunity development.

Once Daily Foscarnet is Effective for HHV-6 Reactivation after Hematopoietic Stem Cell Transplantation

BACKGROUND

Human herpesvirus 6 (HHV-6) reactivation is common after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and is associated with higher mortality and transplant-related complications.

OBJECTIVES

We hypothesized that preemptive treatment with short course of foscarnet at lower cut point of plasma HHV-6 viral load would be effective in treating early HHV-6 reactivation, prevent complications and hospitalization of these patients.

METHODS

We reviewed outcomes of adult patients (18 years or older) who received preemptive treatment with once daily foscarnet 60-90 mg/kg for 7 days for HHV-6 reactivation after allo-HSCT at our institution between 05/2020-11/2022. Plasma HHV-6 viral load was monitored using quantitative polymerase chain reaction twice monthly in the first 100 days post-transplant and twice weekly after reactivation until resolution.

RESULTS

Eleven patients with a median age of 46 years (range, 23-73) were included in the analysis. Ten patients received HSCT from a haploidentical and one patient from HLA matched related donor. The most common diagnosis was acute leukemia (9 cases). Myeloablative- and reduced-intensity conditioning regimens were used in 4 cases and 7 cases, respectively. Most patients (10/11) received post-transplantation cyclophosphamide-based graft-versus-host disease prophylaxis. Median follow-up was 440 days (range, 174-831). Median time to HHV-6 reactivation was 22 days post-transplantation (range, 15-89), median level of viral load 3,100 copies/mL (range, 210-118,000) at first reactivation and median peak viral load was 11,300 copies/mL (range, 600-983,000). All patients received a short course of foscarnet of 90 mg/kg/day (N=7) and 60 mg/kg/day (N=4). Plasma HHV-6 DNA in all patients became undetected after completion of one week treatment. No HHV-6 encephalitis or pneumonitis occurred. All patients achieved neutrophil and platelet engraftment after a median time of 16 (range, 8-22) and 26 (range, 14-168) days, respectively, with no secondary graft failure. No complications related to foscarnet administration were noted. One patient with very high HHV-6 viremia had recurrent reactivation and received a second course of foscarnet as outpatient.

CONCLUSIONS

Short course of once daily foscarnet is effective in treating early HHV-6 reactivation post-transplant, may reduce incidence of HHV-6-related and treatment-related complications, and prevent hospitalization in these patients.

Human Herpesvirus 6 Meningitis in a Neonatal Case

Incidence of human herpesvirus-6 (HHV-6) infection in the neonatal period has been reported in few cases. HHV-6, commonly responsible for roseola, is known to establish infection during infancy and early childhood. A 14-day-old neonate, presented with a fever of 38.3℃, primarily due to an HHV-6 infection, was admitted to our neonatal intensive care unit. A polymerase chain reaction (PCR) of his cerebrospinal fluid was positive for HHV-6. Additionally, serology for HHV-6 PCR was positive. We believe that HHV-6 can cause infection in febrile newborn infants.

Impact of Specific Antibody Level on Human Herpesvirus 6 Reactivation after Allogeneic Stem Cell Transplantation

The majority of adults are seropositive for human herpesvirus 6 (HHV-6). HHV-6 reactivation can occur after allogeneic hematopoietic stem cell transplantation (HSCT) and lead to life-threatening central nervous system disorders. In this prospective study, we evaluated the relationship between HHV-6 reactivation and anti-HHV-6 IgG antibody levels in recipients of allogeneic HSCT. The HHV-6 viral load in the plasma was quantitatively measured weekly after allogeneic HSCT by real-time polymerase chain reaction. The level of anti-HHV-6 IgG antibody was measured by enzyme-linked immunosorbent assay before and serially after transplantation. In 28 of the 56 evaluated patients (50%), HHV-6 reactivation was detected after transplantation. In a multivariate analysis, cord blood as the stem cell source was the only significant factor associated with HHV-6 reactivation (odds ratio, 8.6; 95% confidence interval, 2.3 to 32.6; P < .01). When evaluated in the recipients of cord blood transplantation (CBT), the anti-HHV-6 antibody level before transplantation was significantly lower in the patients with HHV-6 reactivation compared with those without (sample positivity index: median, 2.04 [range, 0.95 to 5.98] versus 4.15 [range, 3.93 to 5.65]; P < .05). The anti-HHV-6 antibody level was significantly decreased at 3 months post-transplantation compared with before transplantation (P < .01). Such differences were not observed in other stem cell sources. Our results demonstrate that the low anti-HHV-6 antibody level before transplantation was associated with the reactivation of HHV-6 after CBT, and that the anti-HHV-6 antibody level was significantly decreased specifically after CBT. These results suggest that HHV-6-specific humoral immunity plays a role in HHV-6 reactivation after CBT.

Herpes virus seroepidemiology in the adult Swedish population

Background

Herpes viruses establish a life-long latency and can cause symptoms during both first-time infection and later reactivation. The aim of the present study was to describe the seroepidemiology of Herpes simplex type 1 (HSV1), Herpes simplex type 2 (HSV2), Cytomegalovirus (CMV), Varicella Zoster virus (VZV) and Human herpes virus type 6 (HHV6) in an adult Swedish population (35–95 years of age).

Methods

Presence of antibodies against the respective viruses in serum from individuals in the Betula study was determined with an enzyme-linked immunosorbent assay (ELISA). Singular samples from 535 persons (53.9% women, mean age at inclusion 62.7 ± 14.4 years) collected 2003-2005 were analyzed for the five HHVs mentioned above. In addition, samples including follow-up samples collected 1988–2010 from 3,444 persons were analyzed for HSV.

Results

Prevalence of HSV1 was 79.4%, HSV2 12.9%, CMV 83.2%, VZV 97.9%, and HHV6 97.5%. Herpes virus infections were more common among women (p = 0.010) and a lower age-adjusted HSV seroprevalence was found in later birth cohorts (p < 0.001). The yearly incidence of HSV infection was estimated at 14.0/1000.

Conclusion

Women are more often seropositive for HHV, especially HSV2. Age-adjusted seroprevalence for HSV was lower in later birth cohorts indicating a decreasing childhood and adolescent risk of infection.

Human herpesvirus 6 and chronic fatigue syndrome

The cause of chronic fatigue syndrome (CFS) is still enigmatic. Using indirect immunofluorescence testing for measuring antibody against human herpesvirus 6 (HHV-6), this study investigated the association of CFS with infection by HHV-6. Seventeen patients (group A) fulfilling the Centers for Disease Control (CDC) definition for CFS were compared with eight patients (group B) with chronic fatigue but not meeting the CDC criteria. No significant difference was found between the two groups for 30 parameters including sex, age, exposure to children and serology for Epstein-Barr virus, cytomegalovirus, herpes simplex virus, and toxoplasma. Univariate analysis showed that patients in group A complained more frequently of a sore throat, headache and of recurrent type of fatigue. These three parameters are discriminant in identifying patients who will meet the CDC case definition of CFS. The titre of antibody against HHV-6 in group A (1:99) was significantly higher than in group B (1:15) (P=0.007). Elevated HHV-6 titres suggests that this virus could be a cofactor in the pathogenesis of CFS.

Seroprevalence of 13 common pathogens in a rapidly growing U.S. minority population: Mexican Americans from San Antonio, TX

Background

Infection risks vary among individuals and between populations. Here we present information on the seroprevalence of 13 common infectious agents in a San Antonio-based sample of Mexican Americans. Mexican Americans represent the largest and most rapidly growing minority population in the U.S., and they are also considered a health disparities population.

Methods

We analyzed 1227 individuals for antibody titer to Chlamydophila pneumoniae, Helicobacter pylori, Toxoplasma gondii, cytomegalovirus, Epstein-Barr virus, herpes simplex virus-1, herpes simplex virus-2 (HSV-2), human herpesvirus-6 (HHV-6), varicella zoster virus (VZV), adenovirus-36, hepatitis A virus, and influenza A and B. Seroprevalence was examined as a function of sex, age, household income, and education.

Results

Seroprevalence estimates ranged from 9% for T. gondii to 92% for VZV, and were similar in both sexes except for HSV-2, which was more prevalent in women. Many pathogens exhibited a significant seroprevalence change over the examined age range (15-94 years), with 7 pathogens increasing and HHV-6 decreasing with age. Socioeconomic status significantly correlated with serostatus for some pathogens.

Conclusions

Our findings demonstrate substantial seroprevalence rates of these common infections in this sample of Mexican Americans from San Antonio, Texas that suffers from high rates of chronic diseases including obesity and type-2 diabetes.

Human Herpesvirus 6 Infection in Hemodialysis and Peritoneal Dialysis Patients

Background

Human herpesvirus 6 (HHV-6) infection occurs worldwide and can be reactivated from latency during periods of immunosuppression, especially after organ transplantation. No previous study has evaluated the influence of dialysis type on HHV-6 infection. The aim of the present study was to determine the prevalence of HHV-6 antibodies in hemodialysis (HD) and peritoneal dialysis (PD) patients.

Methods

W e studied 36 PD patients, 35 HD patients, and 20 healthy subjects, all with no history of organ transplantation. After systematic inquiries and a physical examination, blood was drawn for determination of biochemical parameters, cytomegalovirus immunoglobulin M (IgM) and immunoglobulin G (IgG), hepatitis B surface antigen, and the hepatitis C and human immunodeficiency virus antibodies. Titers of HHV-6 IgM and IgG antibodies were determined by ELISA.

Results

Titers for HHV-6 IgM antibody were positive in 9 HD patients (25.7%), 8 PD patients (22.2%), and 2 control subjects (10.0%, p > 0.05). More HD patients (20.0%) than PD patients (5.6%, p = 0.07) or control subjects (0.0%, p =0.03) were positive for HHV-6 IgG antibody. In HD patients, HHV-6 IgG seropositivity and duration of dialysis were positively correlated (R = 0.33, p = 0.05).

Conclusions

Infection with HHV-6 is not rare in PD and HD patients. In addition, HHV-6 IgG seropositivity was significantly higher in H D patients than in control subjects and approached significance when compared with seropositivity in PD patients. Moreover, in HD patients, HHV-6 IgG seropositivity correlated with duration on HD. These preliminary findings provide insight into the pre-transplantation period for patients and may aid our understanding of how to best protect patients against HHV-6 after transplantation.

Herpes viruses in transplant recipients: HSV, VZV, human herpes viruses, and EBV

The herpes viruses are responsible for a wide range of diseases in patients following transplant, resulting from direct viral effects and indirect effects, including tumor promotion. Effective treatments and prophylaxis exist for the neurotropic herpes viruses HSV-1, HSV-2, varicella zoster virus, and possibly HHV-6. Antivirals seem to be less effective at prevention of the tumor-promoting effects of Epstein-Barr virus and HHV-8. Reduction in immunosuppression is the cornerstone to treatment of many diseases associated with herpes virus infections.

High incidence of human herpesvirus 6 infection with a high viral load in cord blood stem cell transplant recipients

Human herpesvirus 6 (HHV-6) infection in recipients of cord blood stem cell transplants (CBSCTs) was estimated by semiquantitative and real-time quantitative polymerase chain reaction (PCR) and reverse-transcription PCR. Of the CBSCT recipients, 7 (70%) of 10 had active HHV-6 infection after transplantation, and all 7 were inferred from their age to have already had a primary infection. Because HHV-6 DNA is seldom detected in cord blood, these cases were considered likely to represent reactivation. In contrast, the 3 patients without HHV-6 infection were all believed to be naive regarding HHV-6 primary infection because of their age and the results of PCR assays given before the transplantation procedure. The incidence of HHV-6 infection after transplantation was significantly higher (P < .05) than after bone marrow (BM) transplantation and peripheral blood stem cell (PBSC) transplantation, when recipients without primary HHV-6 infection prior to transplantation were excluded (CBSCT, 100%; BMT/PBSCT, 56.3%). Real-time PCR revealed a higher level of viral DNA in the peripheral blood mononuclear cells from CBSCT recipients than from BMT/PBSCT recipients or patients with exanthem subitum (P < .05). HHV-6 mRNA of the U79/80gene was also detected by reverse-transcription PCR in all analyzed patients with HHV-6 infection. Its detection was correlated with the emergence of viral DNA in the plasma and symptoms such as fever and rash. Thus, HHV-6 infection was more frequent and the viral load was higher in CBSCT recipients with prior primary infection.

High incidence of human herpesvirus 6 infection with a high viral load in cord blood stem cell transplant recipients

Human herpesvirus 6 (HHV-6) infection in recipients of cord blood stem cell transplants (CBSCTs) was estimated by semiquantitative and real-time quantitative polymerase chain reaction (PCR) and reverse-transcription PCR. Of the CBSCT recipients, 7 (70%) of 10 had active HHV-6 infection after transplantation, and all 7 were inferred from their age to have already had a primary infection. Because HHV-6 DNA is seldom detected in cord blood, these cases were considered likely to represent reactivation. In contrast, the 3 patients without HHV-6 infection were all believed to be naive regarding HHV-6 primary infection because of their age and the results of PCR assays given before the transplantation procedure. The incidence of HHV-6 infection after transplantation was significantly higher (P < .05) than after bone marrow (BM) transplantation and peripheral blood stem cell (PBSC) transplantation, when recipients without primary HHV-6 infection prior to transplantation were excluded (CBSCT, 100%; BMT/PBSCT, 56.3%). Real-time PCR revealed a higher level of viral DNA in the peripheral blood mononuclear cells from CBSCT recipients than from BMT/PBSCT recipients or patients with exanthem subitum (P < .05). HHV-6 mRNA of the U79/80gene was also detected by reverse-transcription PCR in all analyzed patients with HHV-6 infection. Its detection was correlated with the emergence of viral DNA in the plasma and symptoms such as fever and rash. Thus, HHV-6 infection was more frequent and the viral load was higher in CBSCT recipients with prior primary infection.

Human herpes virus 6 and multiple sclerosis

OBJECTIVES

To systematically review the published evidence for a relationship between human herpes virus 6 (HHV-6) and multiple sclerosis (MS).

MATERIALS AND METHODS

The medical literature was searched using MEDLINE and the Cochrane database. Retrieved studies are presented according to the experimental technique(s) used. The studies are rated for quality using a priori defined criteria.

RESULTS

Twenty-eight studies were retrieved. A total of 12 different experimental techniques were used. Four of these techniques provided evidence for a relationship between HHV-6 and MS, but none were able to show a causative relationship.

CONCLUSIONS

The available literature provides some support for a relationship between HHV-6 and MS. The limitations of the available studies and directions for future research are discussed.

Persistent lack of human herpesvirus-6 specific T-helper cell response in liver transplant recipients

BACKGROUND

Specific immunologic defects predisposing to human herpesvirus-6 (HHV-6), e.g. the role of HHV-6 specific T-helper cell memory response in liver transplant recipients, have not been assessed.

METHODS

T-helper function (mitogen ConA response) as a marker of overall immunocompetence and T-helper response (memory response) specific to HHV-6 and cytomegalovirus (CMV) were assessed in 15 liver transplant recipients and compared with 25 healthy subjects. Samples were tested pretransplant, at 2 weeks, 1 month, 2-3 months, and 1 year posttransplantation. Stimulation index (SI) >3 was considered a positive response.

RESULTS

Seven percent (1/15) of the transplant recipients at any time posttransplantation, as compared to 64% (16/25) of the healthy subjects, had a positive HHV-6 memory response (P = 0.00065). HHV-6-specific memory response in transplant recipients at 2 weeks (SI 1.43), 1 month (SI 1.1), and 2-3 months (SI 1.3) was significantly more suppressed than in healthy subjects (SI 17.5, P = 0.0001). Although transplant recipients as compared to healthy subjects also had a lower CMV-specific memory response posttransplant (P = 0.0439), CMV-specific memory response recovered significantly at 1 month (P = 0.03) and at 2-3 months (P = 0.027) as compared to that at 2 weeks. However, HHV-6 memory response was persistently absent up to 2-3 months with partial recovery at 1 year; 7% of the patients at 2-3 months, but 25% at 1 year had a positive HHV-6 specific memory response. Forty percent (6/15) of the patients developed HHV-6 viremia a mean of 4 weeks posttransplant. Patients with HHV-6 viremia had greater suppression of HHV-6 memory response at 1 month than those without viremia (mean SI, 0.96 vs. 1.3, P = 0.08). All but one of the patients had a positive ConA response.

CONCLUSION

Prolonged suppression of HHV-6 memory response, but not overall T-helper cell function was documented and may play a role in the pathogenesis of HHV-6 infection in liver transplant recipients. Memory response to CMV after liver transplantation was significantly more robust than to HHV-6.

Seroprevalence of human herpesvirus 6 in Andino Puneños (Argentina)

We carried out a seroepidemiological survey to define the prevalence of human herpesvirus 6 (HHV6) infection in an aboriginal population (Andino Puneños) from a remote region in north-west Argentina. Antibodies against HHV6 (total IgG and the 4 subclasses of IgG) were studied in 84 serum samples (collected in 1995 and stored at -70 degrees C), using core blood mononuclear cells infected with HHV6 in an immunofluorescence assay. Of the 84 samples, 70 (83%; 95% confidence interval, 75-91%) exhibited IgG antibodies against HHV6. No significant differences in the frequency of humoral immunity were found among the 4 age-groups studied (mean ages 13, 31, 47 and 70 years) namely, 75%, 89.7%, 79.2% and 100%, respectively. HHV6-specific IgG1 was found in all the positive serum samples tested but none of them contained specific IgG2, IgG3 and IgG4. These results confirmed a high rate of infection with HHV6 within this aboriginal group in Argentina and an IgG1 anti-HHV6 activity compatible with a maintenance of immunity.

Outbreaks of human-herpes virus 6 (HHV-6) infection in day-care centers in Belém, Pará, Brazil

A total of 730 children aged less than 7 years, attending 8 day-care centers (DCCs) in Belém, Brazil were followed-up from January to December 1997 to investigate the occurrence of human-herpes virus 6 (HHV-6) infection in these institutional settings. Between October and December 1997 there have been outbreaks of a febrile- and -exanthematous disease, affecting at least 15-20% of children in each of the DCCs. Both serum- and- plasma samples were obtained from 401 (55%) of the 730 participating children for the detection of HHV-6 antibodies by enzyme-linked immunosorbent assay (ELISA), and viral DNA amplification through the nested-PCR. Recent HHV-6 infection was diagnosed in 63.8% (256/401) of them, as defined by the presence of both IgM and IgG-specific antibodies (IgM+/IgG+); of these, 114 (44.5%) were symptomatic and 142 (55.5%) had no symptoms (p = 0.03). A subgroup of 123 (30.7%) children were found to be IgM-/IgG+, whereas the remaining 22 (5.5%) children had neither IgM nor IgG HHV-6- antibodies (IgM-/IgG-). Of the 118 children reacting strongly IgM-positive (> or = 30 PANBIO units), 26 (22.0%) were found to harbour the HHV-6 DNA, as demonstrated by nested-PCR. Taken the ELISA-IgM- and- nested PCR-positive results together, HHV-6 infection was shown to have occurred in 5 of the 8 DCCs under follow-up. Serological evidence of recent infections by Epstein-Barr virus (EBV) and parvovirus B19 were identified in 2.0% (8/401) and 1. 5% (6/401) of the children, respectively. Our data provide strong evidence that HHV-6 is a common cause of outbreaks of febrile/exanthematous diseases among children attending DCCs in the Belém area.

Human herpesvirus-6 in liver transplant recipients: role in pathogenesis of fungal infections, neurologic complications, and outcome

BACKGROUND

The clinical impact and relevance of human herpesvirus-6 (HHV-6) infection in liver transplant recipients, has not been fully discerned.

METHODS

A prospective study of 80 consecutive liver transplant recipients was performed using surveillance cultures for HHV-6 at weeks 2, 3, 4, and 6 after transplantation. Viral isolation was used for the detection of HHV-6.

RESULTS

HHV-6 infection occurred in 39% (31 of 80) of the patients. Patients with HHV-6 infection were more likely to have hepatocellular carcinoma as underlying liver disease (P=.09). Mental status changes of unidentifiable etiology were significantly more likely to occur in patients with HHV-6 compared with those without (26%, 9 of 31 vs. 6%, 3 of 49, P=.008). HHV-6 infection was an independent predictor of invasive fungal infections (odds ratio 8.3, 95% confidence interval, 1.2-58.0, P=.03). A significant association between HHV-6 infection and CMV infection after transplantation, CMV recipient and donor serostatus, rejection, or fever of unknown origin, could not be documented. Mortality at last follow-up in patients with HHV-6 infection (29%, 9 of 31) was significantly greater than those without HHV-6 (6%, 3 of 49, P=.008).

CONCLUSIONS

Central nervous system complications of unknown etiology after liver transplantation may be related to HHV-6 infection. HHV-6 viremia was an independently significant predictor of invasive fungal infections and was associated with late mortality in liver transplantation recipients.

Serum IgG antibodies to human herpesvirus-6 (HHV-6) do not predict the progression of HIV disease to AIDS. Italian Seroconversion Study group

OBJECTIVES

To evaluate if different levels of human herpesvirus 6 (HHV-6) antibodies can predict HIV disease progression.

DESIGN

Longitudinal study of individuals with a documented date of HIV seroconversion.

SETTING

Clinical centers located throughout Italy.

PATIENTS

Individuals who serconverted for HIV between 1983 and 1995 in Italy.

METHODS

Sera were tested for IgG antibodies to HHV-6 using a commercial enzyme immunoassay. A serum sample with an optical density (OD) > or =242 (i.e. the mean value of 10 negative controls +4x standard deviation) was considered as HHV-6 positive; the progression of HIV disease was evaluated estimating the relative hazards (RH) of AIDS (by Cox models) for individuals with higher levels vs. lower levels of HHV-6 antibodies or considering levels of antibodies based on 10% increase of the distribution (deciles). Rates of CD4 decline fitting linear regression were also estimated.

RESULTS

A total of 381 persons were followed for a median time of 4 years (range: 0.15-9 years) following the date of collection of the serum sample. The median OD value of HHV-6 antibodies was 306, with an interquartile range of 241-440 and a range of 48-2330. A slight inverse correlation was found between HHV-6 antibody levels and age of the individual at the time of serum collection (Spearman rank correlation coefficient, -0.16; p = 0.0013). No association was found between HHV-6 and CD4 level or between HHV-6 and CD8 level at the date of serum collection. The unadjusted RH of progression to AIDS was 0.63 (95% CI: 0.42-0.96) for HHV-6 positive individuals vs. HHV-6 negative; when adjusting for possible confounders (CD4, age, pre-AIDS HIV-related pathologies at the date of sera collection, and previous anti-herpes treatment), the RH of AIDS increased to 0.80 (95% CI: 0.51-1.23). No particular association with HIV disease progression was found when using the deciles of the distribution of HHV-6 antibodies. The median CD4 cell loss was 5.0x10(6) cells/l per month among HHV-6 positive individuals and 5.7x10(6) cells/l per month among the others.

CONCLUSIONS

The presence of high levels of HHV-6 antibodies does not seem to predict the clinical or immunologic progression of HIV disease.

Human herpesvirus 6

Human herpesvirus (HHV) 6 is a beta-herpes, DNA virus. This virus shows closest homology with cytomegalovirus and HHV-7. Infection usually occurs in infants 6 to 24 months of age, and primary infection may result in roseola. HHV-6 infection in infants is the commonest cause of fever-induced seizures. Infection in adults is seen primarily in immunocompromised hosts with solid organ transplants or in those with human immunodeficiency virus infection. The virus is capable of pronounced interaction in vitro with cytomegalovirus and human immunodeficiency virus and induces immunosuppression and apoptosis. The importance of these interactions in vivo necessitates further investigation. HHV-6 infection may contribute to the pathogenesis of multiple sclerosis. HHV-6 may be diagnosed by viral culture, serology, or polymerase chain reaction.

Cytomegalovirus and human herpesvirus 6 both cause viral disease after renal transplantation

BACKGROUND

Systemic viral disease after renal transplantation, especially after treatment with OKT3 or antithymocyte globulin, has usually been attributed to cytomegalovirus (CMV) infection. Identification of human herpesvirus 6 (HHV6) has raised the possibility that infection or reactivation of this virus may also occur in the same setting.

METHODS

We thus examined the incidence of CMV and HHV6 infection in a prospective blinded consecutive series of 30 renal and renal/pancreas transplant patients, 22 of whom received OKT3, antithymocyte globulin, or both.

RESULTS

Clinical diagnosis of a viral syndrome was made in 15 patients. Three patients with only HHV6 DNA in urine or serum had fever and abnormal liver function but not neutropenia. All five CMV-seronegative patients who received positive kidneys developed moderate to severe disease with fever and neutropenia but also had HHV6 DNA in urine or serum. Seven CMV-seropositive patients developed disease, mostly after OKT3/antithymocyte globulin, but six shed both CMV and HHV6 in urine or serum. The simultaneous detection of both HHV6 and CMV DNA in either urine or serum was the strongest predictor of disease (and also the severity of disease), with an odds ratio of 99.0 (95% confidence intervals 5.4-1814, P<0.002).

CONCLUSION

Most systemic viral disease after renal transplantation may be due to either coinfection or reactivation of CMV and HHV6 together. A wider understanding of risk factors for severe viral disease in this setting may come from testing for both viruses in all donors and patients in both clinical practice and clinical trials.

Human herpesvirus 6 infection and associated pathogenesis following bone marrow transplantation

Human herpesvirus 6 (HHV-6) infections following bone marrow transplantation (BMT) have been shown to be associated with fever, skin rash, graft versus host disease, encephalitis, delay in engraftment, marrow suppression, and pneumonia. Unfortunately several of these studies were case reports and although the results were suggestive they prompted us to study these pathological events systematically. These associations were primarily based on either HHV-6 isolation, HHV-6 DNA detection, antigen detection or increases in HHV-6 specific antibodies. HHV-6 activity was more frequent during the post- rather than the pre-transplantation period. All HHV-6 isolates from BMT patients have been shown to be variant B. A better understanding of HHV-6 associated pathogenesis gained by larger prospective trials is needed to facilitate proper treatment of cases of idiopathic illnesses or those associated with symptoms (fever, skin rash) similar to those caused by HHV-6.

Enzyme-linked immunosorbent assay for detection of antibody to human herpesvirus 6

The results obtained with an enzyme-linked immunosorbent assay (ELISA) for detection of human herpesvirus 6 (HHV-6) immunoglobulin G using a single 1:100 dilution of serum correlated well with those found by an indirect fluorescence microscopic assay (IFA) (r = 0.71). Concordant results were found in all 7 paired serum samples obtained from patients with acute primary infections and in 37 of 41 (90.24%) single serum samples. Fourteen serum samples (25%) which yielded nonspecific results by IFA were evaluable by ELISA. In a serologic survey using the ELISA, a disproportionate number of 12-month-old infants had low difference-of-optical-density values, suggesting that maternal antibody might persist beyond a year of age. This finding and the rises in antibody to HHV-6 found in patients with primary cytomegalovirus infections might lead to overestimation of HHV-6 infection rates in young children in seroprevalence studies. Other herpesvirus infections produced lesser effects on anti-HHV-6.

Benign and malignant smooth muscle tumors containing Epstein-Barr virus in children with AIDS

Smooth muscle tumors (leiomyosarcomas) are the second most prevalent malignancy of children with the acquired immunodeficiency syndrome (AIDS). We have investigated the tumors, plasma, and peripheral white blood cells of eight children with AIDS with smooth muscle tumors for evidence of tumor association with human immunodeficiency virus (HIV) and Epstein-Barr virus (EBV). Very low levels of HIV were found in the tumors of the AIDS patients, probably resulting from blood-borne carriage of virus. These smooth muscle tumors had very high quantities of EBV in all the tumor cells by in situ hybridization, with an average of 4.5 EBV genomes per cell by quantitative polymerase chain reaction amplification. Increased amounts of EBV were found in the peripheral blood cells of two AIDS patients before the time of tumor diagnosis. EBV clonality studies demonstrated different monoclonal EBV infection of two separate colonic tumors from one patient, and dual or mixed monoclonal EBV infection in another patient. The muscle cells of leiomyomas and leiomyosarcomas of patients with AIDS demonstrated prominent staining with antibodies to the EBV receptor. The uniform distribution and striking amount of EBV in the tumor cells demonstrates that EBV is capable of infecting smooth muscle cells and that these cells support EBV replication. Clonal EBV proliferation suggests that EBV infection occurs at an early stage of tumor development. These findings indicate that EBV has a causal role in the oncogenesis of leiomyosarcomas of patients with AIDS.

Prevalence of human herpesvirus 6 antibody in the population of Belém, Pará, northern Brazil

A total of 497 serum samples obtained from residents of 2 neighbourhoods (Terra-Firme and Guamá) in Belém, Pará, Brazil was tested for the presence of antibody to human herpesvirus 6 (HHV6), using an indirect immunofluorescence assay. The overall seroprevalence was 90%, with seropositivity rates ranging from 75% to 100% in the different age groups and sexes. There was a significant difference between the antibody prevalences in Terra-Firme and Guamá, 94% and 87%, respectively (P = 0.01). The geometric mean titres (GMT) of antibody to HHV6 declined from the first (< or = 2 years) to the sixth (31-40 years) age groups, and slightly increased (GMT > 50) among individuals older than 40 years.

Human herpesvirus 6

Human herpesvirus 6 variant A (HHV-6A) and human herpesvirus 6 variant B (HHV-6B) are two closely related yet distinct viruses. These visuses belong to the Roseolovirus genus of the betaherpesvirus subfamily; they are most closely related to human herpesvirus 7 and then to human cytomegalovirus. Over 95% of people older than 2 years of age are seropositive for either or both HHV-6 variants, and current serologic methods are incapable of discriminating infection with one variant from infection with the other. HHV-6A has not been etiologically linked to any human disease, but such an association will probably be found soon. HHV-6B is the etiologic agent of the common childhood illness exanthem subitum (roseola infantum or sixth disease) and related febrile illnesses. These viruses are frequently active and associated with illness in immunocompromised patients and may play a role in the etiology of Hodgkin's disease and other malignancies. HHV-6 is a commensal inhabitant of brains; various neurologic manifestations, including convulsions and encephalitis, can occur during primary HHV-6 infection or in immunocompromised patients. HHV-6 and distribution in the central nervous system are altered in patients with multiple sclerosis; the significance of this is under investigation.

Comparison of HHV-6 antibody titers in West Africa and the Caribbean

Human herpesvirus-6 (HHV-6) infection seems to be ubiquitous early in life, but antibody responses vary by geographic area. We compared HHV-6 antibody titer in 123 West African and 122 Caribbean serum samples. A quantitative immunofluorescence assay (IFA) using antigens derived from an HSB-2 cell line was used to test for IgG HHV-6 (GS strain) antibodies. The prevalence of HHV-6 antibodies was high (98%) in both sites. African samples had a significantly higher geometric mean titer (GMT: 697) than did Caribbean samples (GMT: 99). There was no difference between males (GMT: 260) and females (GMT: 270) overall. Children up to and including 9 years old had significantly higher titers (GMT: 483) than did all others (GMT: 237), and female children tended to have higher titers than did male children. In both areas there was a trend towards highest titer at younger age, followed by a decrease in titer during adulthood and middle age, and a secondary rise in titer in the oldest age group. Environmental and host factors may explain these geographic differences in antibody responses between two groups of African origin.

Human herpesvirus 6

HHV-6, the first T-lymphotropic human herpesvirus, is an important novel human pathogen. It is the cause of exanthem subitum in infants and may act as an opportunistic agent in immunocompromised patients. Moreover, several lines of clinical and experimental evidence suggest that HHV-6 may accelerate the progression of HIV infection. Progress in the study of HHV-6 has been rapid, in part as a consequence of the strong current interest in human lymphotropic viruses and their relationship with the immune system. Nonetheless, the full spectrum of diseases linked to this agent is still unknown (Table 2) and animal models of infection have not yet been exploited. The next few years will be crucial for a complete understanding of the potential role of HHV-6 in human disease.

Low-incidence latent infection with variant B or roseola type human herpesvirus 6 in leukocytes of healthy adults

Nested primer-based polymerase chain reaction was employed to determine the frequency of latent infection with human herpesvirus 6 (HHV-6) among healthy adults from Bratislava, Slovak Republic. A 592-bp region, upstream from the gene encoding the putative large tegument protein of HHV-6, was amplified from DNA extracted from peripheral blood mononuclear cells (PBMC) of only one of 29 seropositive adults, suggesting that as few as 1 in 10(5) PBMC may be infected with the virus. Direct sequencing of the 592-bp fragment indicated that the virus harbored by the seropositive Slovak subject (designated B38) differed by only 3 nucleotides from an HHV-6 variant B strain (R-147) isolated from an American infant with a roseola-like illness and by 32 bases from the variant A strain GS isolated from a patient with lymphadenopathy (5.4% sequence divergence). None of these strains had a deoxyadenosine at base position 1251, when compared to the published sequence of strain GS clone pZVH14. Although this discrepancy did not affect the large tegument protein gene, it altered the predicted amino acid sequences of two putative proteins coded by open-reading frames 1 and 2 (ORF 1 and ORF 2) located upstream from this gene.

Serological response of paediatric oncology patients to human herpesvirus-6

The serological response of paediatric oncology patients to human herpesvirus-6 (HHV-6) was investigated at presentation and during treatment. Sera from 66 patients presenting with malignancy and 66 controls were examined for anti-HHV-6 IgG by indirect immunofluorescence test (IFA) and enzyme linked immunosorbent assay (ELISA), and for anti-HHV-6 IgM by IFA. Serial samples from 45 children on chemotherapy were examined for anti-HHV-6 IgG by ELISA and sera from selected patients on chemotherapy were examined for IgM by IFA. The response of these patients to four other herpesviruses was also investigated. Ninety percent of presenting patients and controls were IgG positive for HHV-6 by IFA and ELISA. Anti-HHV-6 IgG as measured by the HHV-6 ELISA index declined over time in patients on chemotherapy. Two presenting controls and one leukaemic child with a primary cytomegalovirus seroconversion were anti-HHV-6 IgM positive. In the patient group seropositivity to herpesviruses (types 1-6) increased with age, the mean age of those with IgG to HHV-6 alone was 3.7 years compared to 6.8 years for those with antibodies to all five viruses. At the time of presentation paediatric oncology patients have a similar serological response to HHV-6 as age-matched controls and this IgG response wanes with treatment. Whether this is significant in terms of viral pathogenicity is not known and will require investigation of viral activity in these patients.

Molecular epidemiological studies of human herpesvirus 6 in families

The mode of transmission of human herpesvirus 6 (HHV-6) was investigated by molecular epidemiological techniques in four families. HHV-6 was isolated from the peripheral blood of seven infants with exanthem subitum, including siblings, and from the saliva of two mothers. These isolates were examined for genetic relatedness by means of restriction enzymes analysis of purified DNA. While the profiles of the digestion patterns differed among families, they were very similar in a particular family. These results may suggest that HHV-6 is transmitted primarily from mother to child.

Prevalence of human herpesvirus 6 antibody among isolated Amazonian Amerindian communities in Brazil

Human herpesvirus 6 (HHV6) antibody was detected by the anticomplement immunofluorescence test in 65 of 592 serum samples (10.9%) obtained from Amerindians belonging to 4 remote communities inhabiting the Amazon Region of Brazil. Seropositivity rates ranged from 5.4% in the Oyampí to 14.9% in the Tucano. Among the Mekranoiti and Tiriyo, the seroprevalence rates were 12.5% and 11.8%, respectively. In children aged 0-10 years, the prevalences of HHV6 antibody ranged from 5.2% to 24.2%, among the Oyampí and Mekranoiti tribes, respectively. In the 11-20 and > 20 years old age groups, percentages of positivity ranged, in the former group, from 9.5% to 17.5% in the Oyampí and Tucano, respectively and, in the latter group, from 1.3% in the Oyampí to 14.8% in the Tucano. The prevalences of HHV6 antibody decreased regularly through the first 3 age-groups in the Mekranoiti and Tiriyo. In addition, frequencies of seropositivity were consistently higher in males than in females in the Mekranoiti (P < 0.05), Oyampí and Tiriyo tribes.

Human herpesvirus 6 is present in lesions of Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is a disease characterized by Langerhans cell infiltration of skin and bone, with its most severe form manifested by multifocal infiltration of many organs. The etiology is unknown, although viral infection has been proposed as a potential pathogenic factor. Human herpesvirus 6 (HHV-6), a recently described member of the human herpesvirus family, has been associated with atypical or malignant lymphocytic processes, and immune disorders. Based on these observations, we suspected that HHV-6 may play a role in the pathogenesis of LCH. Lesional tissue of 30 patients with LCH was retrospectively examined for the presence of HHV-6 by using the polymerase chain reaction. Tissue specimens from 63 patients with other benign and malignant histiocytic and lymphocytic diseases served as controls. In addition, all specimens were examined with control primers specific for herpes simplex virus (HSV). HHV-6 DNA was detected in lesions of 14 of 30 patients with LCH (47%). On clinical subgroup analysis, HHV-6 DNA was found in 10 of 16 patients with extraosseous disease (63%) and in four of 14 patients with disease limited to bone (29%). In each case, the prevalence of HHV-6 in LCH lesions was statistically significant, when compared to the control population. HSV DNA was not found in any of the LCH or control specimens. Although the presence of a virus alone does not establish a causal role in the disease, it supports the possibility of an etiologic relationship. From this study, we emphasize the need for further investigation of the potential HHV-6-mediated pathogenesis of LCH.

Human herpesvirus 6 and multiple sclerosis: survey of anti-HHV-6 antibodies by immunofluorescence analysis and of viral sequences by polymerase chain reaction

A possible involvement of human herpesvirus 6 (HHV-6) infection in the pathogenesis of multiple sclerosis (MS) was investigated. The immunofluorescence analysis of sera from 126 MS patients showed significantly higher anti-HHV-6 antibody titres in MS sera than in 500 normal controls. A polymerase chain reaction (PCR) assay of the peripheral blood mononuclear cell (PBMC) DNAs of 31 MS patients and 24 normal subjects was positive in one normal control and in one MS patient. The Southern blot analysis indicated an unexpectedly high level of viral sequences in the MS patient, but not in the control. Since viral sequences are rarely present in MS subjects, the high anti-HHV-6 antibody titres found in MS are likely to be related to immune impairment rather than reactivation of a latent infection.

Growth characteristics of human herpesvirus-6: comparison of antigen production in two cell lines

In order to optimize viral antigen production, the growth characteristics of human herpesvirus-6 (HHV-6) (strain AJ) were studied in two cell lines: HSB-2 and JJHAN. The cells were infected with different multiplicities of infection (moi) and viral growth was monitored by appearance of cytopathic effect (CPE), total and viable cell count, immunofluorescence test, immunoblotting, and electron microscopy. Although > or = 70% of JJHAN cells showed CPE when infected at high moi, only 5% of the cells contained viral antigens when tested with immunofluorescence. In contrast the percentage of cells showing fluorescence in HSB-2 cells reached > or = 30% when infected at > or = 1:50. More than 10 polypeptides of molecular weight ranging between 31-140 kD appeared in the HSB-2 cultures by immunoblotting while only 3 polypeptides were detected in the JJHAN cultures at high moi. Different stages of virus maturation were seen in the HSB-2 cells by electron microscopy but the replication of the virus in JJHAN cells appeared to be restricted. For the purpose of antigen production the optimal conditions for the AJ strain of HHV-6 were found to be culturing in HSB-2 cells at a concentration of 1:25-1:50 infected to uninfected cells and harvesting after 7 days.

IgG antibodies to human herpesvirus-6 in young children: changes in avidity of antibody correlate with time after infection

Sera from 321 children aged 0-179 weeks and 196 adult blood donors were examined for IgG antibodies to human herpesvirus-6 (HHV-6) using an indirect immunofluorescence test. After birth, antibody prevalence declined to a minimum between 20 and 29 weeks. Thereafter the percentage of individuals with antibody increased up to the age of 60-69 weeks after which the prevalence of antibody in the children remained stable at about 88%; in contrast, the seroprevalence in blood donors was 98%, indicating that some individuals remain susceptible to infection after early childhood but that virtually all are infected by the time they reach adulthood. The HHV-6 antibody titre increased steadily over the first 70 weeks of life and then remained stable up to 179 weeks old at a level significantly higher than that of the adults. Two hundred and eighteen of the 321 sera whose HHV-6 antibody titres were 40 or greater were tested for antibody avidity using a modification of the immunofluorescence test whereby low avidity antibody was eluted with urea. The results show that the age distribution of low avidity antibody closely parallels the known distribution of exanthem subitum and, moreover, that the mean antibody avidity increased with time after primary infection. The method was further validated because well-characterised convalescent sera taken from seven children within 3 weeks of exanthem subitum all contained low avidity antibodies. The data presented in this study indicate that low avidity IgG to HHV-6 may be detected after primary infection and that this should prove useful in diagnosis and for seroepidemiological surveys.

Human herpesvirus-6 infections in infants admitted to hospital

Virological studies were carried out on 3 to 36-month-old patients admitted to the Children's Hospital of the University of Modena with febrile syndrome from September 1990 to February 1991. Virological tests were carried out for human herpesvirus-6 (HHV-6), Epstein-Barr virus (EBV), cytomegalovirus (CMV), herpes simplex virus 1 (HSV-1), adenoviruses, parainfluenza viruses 1, 2 and 3, respiratory syncytial virus (RSV) and influenza viruses A and B. Viral infections were confirmed in 60.7% patients: 39.6% were correlated with HHV-6, 5.4% with EBV, 5.4% with both HHV-6 and EBV, 5.4% with adenoviruses, 1.8% with HSV-1, 1.8% with CMV and 1.8% with an unidentified herpes-like lymphotropic virus. HHV-6 isolates were obtained from either peripheral blood lymphocytes (PBLs) or pharyngeal secretion of the infected children. HHV-6 infections included both primary infections (72%) and reactivations (28%). Among HHV-6 infected children, 40%, with exanthem subitum, had infections presenting serological evidence of primary infection and virus isolation from PBLs. The remaining cases of primary infection and the cases of reactivation were found in patients with febrile syndrome without rash (60%). HHV-6 isolates were obtained either from PBLs or pharyngeal secretions from these patients. Southern blot hybridization of the DNAs of 4 HHV-6 isolates showed that the circulating HHV-6 strains all appeared similar, but differed from the HHV-6 strain U1102 used as a positive control.

Avidity of IgG antibodies to human herpesvirus-6 distinguishes primary from recurrent infection in organ transplant recipients and excludes cross-reactivity with other herpesviruses

A newly developed IgG antibody avidity test for human herpesvirus-6 (HHV-6) was used in a study of primary and recurrent HHV-6 antibody responses in immunocompromised solid organ graft recipients. In a primary HHV-6 infection low avidity antibody was detected which matured to high avidity within 5 months whereas, in contrast, high avidity antibody was found in three recurrent infections thus showing the ability of the test to discriminate between primary and recurrent infection in immunosuppressed patients. Six HHV-6 seropositive transplant patients who experienced a subsequent primary human cytomegalovirus (CMV) infection had high avidity concurrent HHV-6 antibody rises, thus excluding a cross-reaction from the low avidity antibodies generated in the primary CMV response and providing evidence of recurrent HHV-6 infection. Four further HHV-6 seropositive patients with proven primary Epstein-Barr virus (EBV) infection were also studied; in each of these cases high avidity HHV-6 antibody rises were seen likewise suggesting recurrent HHV-6 infection. The test is therefore of value in the investigation of herpesvirus infections in transplant patients.

Prevalence of herpesvirus, human T-lymphotropic virus type 1, and treponemal infections in Southeast Asian refugees

Sera obtained for treponemal serology (VDRL) from 193 Southeast Asian refugees representing five ethnic groups seen in a primary care clinic were examined for antibodies to human T-lymphotropic virus type 1 (HTLV-1), human herpes-virus-6 (HHV-6), Epstein-Barr virus (EBV), and cytomegalovirus (CMV). The seroprevalence was highest for EBV (99%), followed in decreasing order by CMV (95%), HHV-6 (26%), and HTLV-1 (0.6%). The VDRL was positive in 15% of patients. The highest seroprevalence to HHV-6 was noted in the Chinese (33%) and the lowest in the Laotian hilltribes, the Mien and Hmong (14%). Antibody to HHV-6 was most prevalent among patients under 20 and those between 60 and 69 years of age. Differences were not found among ethnic groups in the seroprevalence of HTLV-1, EBV, or CMV.

Human herpesvirus-6 infection and bone marrow transplantation

Human herpesvirus-6 (HHV-6) is ubiquitous in the human population and causes exanthem subitum, a benign disease seen in infancy. However it also produces a wide spectrum of clinical manifestations including cases with a fatal outcome. The virus remains latent in several organs, including the kidneys, liver, lymph/nodes and salivary glands, after the primary infection and reactivates when immune function is impaired. Reactivation of the virus occurred in a half of the bone marrow recipients 2 to 4 weeks after bone marrow transplantation (BMT). It remains to be established whether HHV-6 in fact causes the fever and rash observed in recipients who have reactivation of the virus. The data reviewed here will be required to compare with those of human herpesvirus 7 and a different group of HHV-6.

Seroprevalence of antibodies against human herpesvirus 6 in the Quebec City area

Seroprevalence of antibodies against human herpesvirus 6 was determined in a sample of 303 randomly selected individuals from the Quebec City area. The influence of different variables on antibody litres was also evaluated. Human herpesvirus 6 was grown in the HSB-2 cell line, and antibody litres were measured by indirect immunofluorescence. Serum samples were collected from 177 females and 126 males ranging in age from two months to 88 years. Ninety-nine per cent (300 of 303) of this population had an antibody titre of at least 1:10, whereas 75% had a titre of at least 1:80. Women had a higher geometric mean litre than men (P=0.06). This difference between sexes varied according to age and became statistically significant in subjects older than 20 years of age (P=0.04). It was found that this difference was attributable to higher antibody litres in women in the 15 to 40 year age group who had previously had children.

Gene for the major antigenic structural protein (p100) of human herpesvirus 6

A human herpesvirus 6 (HHV-6) structural protein of 100 kDa (p100) is the polypeptide most frequently and intensively reactive in immunoblotting analyses with human sera on HHV-6-infected cells or partially purified virions. The gene for p100 was identified by screening a bacteriophage lambda library with monospecific rabbit antisera. The gene codes for a polypeptide of 870 amino acids with a calculated molecular size of 97 kDa. Its amino-terminal third is weakly homologous to the immunogenic basic matrix phosphoprotein pp150 of human cytomegalovirus. Five fragments representing more than 93% of HHV-6 p100 were prokaryotically expressed. The antigenic epitopes of p100 were preliminary mapped by immunoblotting with human sera. They are located within the carboxy-terminal part which is neither homologous nor cross-reactive to pp150 of human cytomegalovirus. Availability of the gene for the immunodominant structural protein should provide tools for studies of pathogenesis by HHV-6.

Primary human herpesvirus 6 infection in young children

BACKGROUND

Human herpesvirus 6 (HHV-6) is a recently discovered virus that, on the basis of serologic evidence, appears to infect most children by the age of three years. However, the clinical manifestations of primary HHV-6 infection have not been well defined.

METHODS

We studied consecutive children two years old or younger who presented to an emergency ward with febrile illnesses. Our evaluation included the isolation of HHV-6 from peripheral-blood mononuclear cells, an immunofluorescent-antibody assay, the detection of HHV-6 by the polymerase chain reaction (PCR), and restriction-endonuclease-fragment profiles of HHV-6 isolates.

RESULTS

HHV-6 was isolated from 34 of 243 acutely ill children (14 percent). The children with viremia had irritability, high temperatures (mean, 39.7 degrees C), and inflammation of tympanic membranes (in 21), but few other localizing signs. Two children were hospitalized, but all 34 recovered after an average of four days of fever. The rash characteristic of roseola, which has been associated with HHV-6 infection, was noted in only three children. In 29 children (85 percent), serum samples obtained during convalescence had at least a fourfold increase in IgG antibody titers; 4 infants less than three months old who presumably had maternal antibody did not have this increase. HHV-6 was isolated from blood obtained during convalescence in only one child, but in two thirds of the children the virus could be detected by PCR. The isolates had genomic heterogeneity, indicating the presence of multiple strains.

CONCLUSIONS

Primary infection with HHV-6 is a major cause of acute febrile illness in young children. Such infection is associated with varied clinical manifestations, viremia, and the frequent persistence of the viral genome in mononuclear cells.

IgM neutralizing antibody responses to human herpesvirus-6 in patients with exanthem subitum or organ transplantation

The assay for detecting IgM neutralizing (NT) antibody activity to human herpesvirus-6 (HHV-6) was developed by using pretreatment of blood sample with staphylococcal protein A. The activity was mostly present in IgM fractions of serum but not in IgA fractions separated by ultracentrifugation. The assay was used for seroepidemiological studies for HHV-6 infection. In primary HHV-6 infection, IgM NT antibodies appeared 5 to 7 days after onset of exanthem subitum, reached maximum titers at 2 to 3 weeks, and tended to decline to undetectable levels after 2 months. In contrast, reactivation of HHV-6 observed in organ transplants showed somewhat greater degree of IgM NT antibody responses that persisted for 2 to 3 months and became undetectable 5 to 6 months after transplantation. The level and persistence of NT antibody titers measured by the conventional method was generally greater than those of the IgM titers. The prevalence of the IgM NT antibodies was examined in healthy individuals. The antibody was first detected at 4 to 7 months of age (5%), reached maximum level at 8 to 11 months (40%), and was detectable by 4 to 6 years (17%). A few (4 to 5%) of adolescents and adults were positive for the antibody.