Human herpesvirus 6 in monocytes of transplant patients

Human herpesvirus 6 is an important pathogen in infectious lung disease after allogeneic bone marrow transplantation

Two hundred and ten bronchoalveolar lavage (BAL) samples were obtained from 50 patients 10 days before and on defined days after allogeneic bone marrow transplantation (BMT). The samples were examined for human cytomegalovirus (HCMV) and human herpesvirus-6 (HHV-6) by polymerase chain reaction (PCR). Fifteen patients (30%) had a positive result for HCMV in at least one sample and 25 (50%) were positive for HHV-6 in at least one sample. Five patients developed HCMV-associated interstitial pneumonia (HCMV-IP) within 100 days after allogeneic BMT. Four of these patients were positive for both HCMV and HHV-6. Conspicuous HHV-6 positivity was detected in BAL samples obtained because of respiratory symptoms. No association was found between detection of HHV-6 and acute graft-versus-host disease. Engraftment failure or a delay in engraftment was observed in none of the 50 patients. The data from this study indicate that HHV-6 is a pathogen in HCMV-associated, as well as in non-HCMV-associated infectious lung disease after BMT.

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.

A method for detection of HHV-6 antigens and its use for evaluating antiviral drugs

A simple and reproducible method for detection of human herpesvirus 6 (HHV-6) antigens was developed using a dot blot assay in order to assess virus titer and to evaluate the effect of antiviral drugs against HHV-6. The titer of virus stocks obtained by the dot blot assay was the same as that determined by an immunofluorescence assay (IFA). This method was then applied to evaluate the effect of several antiviral drugs against HHV-6, including phosphonoformic acid (PFA), 9-(2-hydroxyethoxymethyl)guanine (ACV), 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine (DHPG) and (S)-1-[(3-hydroxy-2-phosphonylmethoxy)propyl]cytosine [(S)-HPMPC]. The end-point concentrations (EPC, which was determined visually) of DHPG and (S)-HPMPC were approximately 1 microgram/ml. These drugs were more effective than the others which had EPCs of approximately 16 micrograms/ml each. The EPC values of four drugs were almost similar to EC90 values determined by measuring density of each dot blot. Thus, the EPC values can be utilized to determine the efficacy of these drugs in the inhibition of HHV-6 replication. The block in virus replication was not due to toxic effect of these drugs on cord blood mononuclear cells (CBMCs). These results suggest that a dot blot method which detects HHV-6 antigens can be useful for titrating virus yield and evaluating antiviral drugs against HHV-6 replication.

Human herpesvirus-6 infection in renal allografts: retrospective immunohistochemical study in Japanese recipients

This study was conducted to determine the incidence and clinical significance of human herpesvirus-6 (HHV-6) infection in renal allografts. A total of 105 biopsy specimens from 72 recipients were immunohistochemically examined for the presence of HHV-6 antigen, which localized in the distal tubular epithelial cells and in a few lymphocytes infiltrating into the interstitium. HHV-6 antigen in the tubular epithelia was detected in 63 (61.2%) specimens. Categorically, a higher incidence of the antigen was noted in specimens of accelerated rejection (3/4, 75.0%), acute rejection (28/3, 73.7%), and cyclosporin nephropathy (8/11, 72.7%). The antigen was present and absent an almost equal number of times in the categories of chronic rejection, intraoperative and routine protocol biopsies. Repeated biopsies were performed in six cases showing HHV-6 antigen, only one of which underwent transplant nephrectomy due to severe chronic rejection. Single or multinucleated giant cells in distal tubuli occurred in 10 (9.5%) specimens in a scattered manner. All of them were diagnosed as acute or chronic rejection. The giant cells showed no immunoreactivity for HHV-6, cytomegalovirus, or herpes simplex virus. These results indicate overall that HHV-6 infection is common in renal allografts and might be reactivated in acute rejection or cyclosporin nephropathy. The presence of HHV-6 antigen, however, does not necessarily correlate with a poor prognosis for the renal graft nor with the occurrence of giant cells in distal tubuli.

Activation of human herpesvirus-6 in children with acute measles

Virological and serological studies were carried out prospectively to evaluate the possible activation of human herpesvirus-6 (HHV-6) in 50 infants and children with acute measles by isolation of HHV-6 from peripheral blood and by determining neutralizing antibodies to the virus. All but 5 patients (90%) were seropositive to HHV-6 in the acute stage of measles and 18 (40%) had a significant increase in HHV-6 antibody titers thereafter, whereas only 2 of 27 patients who were initially seropositive to Epstein-Barr virus (EBV) viral capsid antigen (VCA) had a significant rise in antibody titers to EBV VCA. Among 18 patients with a significant increase in HHV-6 titers, the virus was isolated from the peripheral blood mononuclear cells of three patients in the early convalescent stage of measles. These results indicate that activation of HHV-6 may occur frequently a few weeks after primary infection with the measles virus.

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.

Antigenic relationships among human herpesvirus-6 isolates

Human herpesvirus 6 (HHV-6) prototype isolate GS is a newly identified lymphotropic herpesvirus and several subsequent herpes isolates were recognized as HHV-6 by their hybridization to a HHV-6(GS) DNA probe pZVH14. DNA restriction analysis and in vitro tropism studies show that HHV-6 isolates can be divided into two groups, designated group A and group B. Antigenic relationships among 15 HHV-6 isolates belonging to these two groups were examined using rabbit antibodies against HHV-6(GS) infected cells, 11 monoclonal antibodies against three glycoproteins and four non-glycoproteins of HHV-6(GS), and sera from 136 healthy adults. More than 20 polypeptides from all these isolates were immunoprecipitated by rabbit polyclonal antibodies against HHV-6(GS) infected cells. Reactivities of monoclonal antibodies segregated these isolates into the same two groups. Group A contains HHV-6(GS), HHV-6(U1102) from a Ugandan acquired immunodeficiency syndrome (AIDS) patient, and nine other HHV-6 isolates from various disorders. HHV-6(Z-29) from a Zairian AIDS patient, HHV-6(SF) isolated from the saliva of a human immunodeficiency virus (HIV)-infected individual, HHV-6(OK) from a child with exanthem subitum, and HHV-6(DC) from a leukopenia patient are in group B. Eighty-one percent of the sera showed similar antibody titer in immunofluorescence assay with group A HHV-6(GS) and group B HHV-6(Z-29) infected cells and 19% of the sera showed two- to four-fold antibody titer differences. The mobilities of many of the polypeptides immunoprecipitated from group A HHV-6(GS) and group B HHV-6(Z-29) infected cells were different and sera showed differences in the quantities and nature of polypeptides immunoprecipitated.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the DNA polymerase gene of human herpesvirus 6

The construction of a recombinant bacteriophage lambda library containing overlapping clones covering 155 kbp of the 161-kbp genome of the Ugandan U1102 isolate of human herpesvirus 6 (HHV-6) is described. The use of degenerate-primer polymerase chain reaction allowed the isolation of a DNA probe for the DNA polymerase gene of HHV-6, which was subsequently used to isolate and position the pol gene on the physical map of the viral genome. A 4.4-kbp EcoRI DNA restriction fragment containing the pol gene was isolated and sequenced. The open reading frames flanking the pol gene code for the HHV-6 glycoprotein B gene and the human cytomegalovirus UL53 homolog. This arrangement is different from that seen in the alpha and gamma herpesvirus families, lending further support to the notion that HHV-6 is a member of the beta herpesvirus group.

Identification, characterization, and sequence analysis of a cDNA encoding a phosphoprotein of human herpesvirus 6

Human herpesvirus 6 (HHV-6)-specific monoclonal antibody (Mab) 9A5D12 reacted with the nucleus of HHV-6 strain GS-infected cells and immunoprecipitated a phosphorylated polypeptide with an approximate size of 41 kDa, designated HHV-6 P41. A 110-kDa polypeptide was also immunoprecipitated by the MAb. These polypeptides were synthesized early in infection, and the synthesis was greatly reduced by phosphonoacetic acid. Polypeptides with identical sizes were recognized by the MAb from cells infected with an additional eight HHV-6 strains. A 2.1-kb cDNA insert was identified from an HHV-6(GS) cDNA library constructed in the lambda gt11 expression system by using MAb 9A5D12. This cDNA insert hybridized specifically with viral DNA from HHV-6 strains GS and Z-29 and with two predominant transcripts with approximate sizes of 2.5 and 1.2 kb from infected cells. The reactivity of the MAb with a fusion protein expressed in the prokaryotic vector suggested that the cDNA encodes a 62- to 66-kDa protein. Analysis of the nucleotide sequence of the cDNA insert revealed a 623-amino-acid-residue single open reading frame of 1,871 nucleotides, with an open 5' end. The predicted polypeptide is highly basic and contains a long stretch of highly hydrophobic residues localized to the carboxy terminus. The amino-terminal half of the predicted HHV-6 protein from the cDNA shows significant homology with the UL44 gene product of human cytomegalovirus, coding for the ICP36 family of early-late-class phosphoproteins. Two TATA boxes are located at nucleotide positions 668 and 722 of the cDNA. In vitro translation of RNA transcribed in vitro from the cDNA resulted in the synthesis of a 41-kDa polypeptide only. This polypeptide was readily immunoprecipitated by MAb 9A5D12, and its partial peptide map was identical to that of the 41-kDa polypeptide detected in infected cells. Together, these results indicate that the HHV-6 P41 is encoded within a gene coding for a larger protein.