Two groups of human herpesvirus 6 identified by sequence analyses of laboratory strains and variants from Hodgkin's lymphoma and bone marrow transplant patients

Abstract

Fifteen human herpesvirus 6 (HHV-6) strain variants were analysed by PCR amplifications, restriction enzyme site polymorphism and sequence analyses. Three DNA regions were chosen for study: a fragment of a variable glycoprotein gene (210 bp), the conserved glycoprotein H (gH) gene complete with intergenic sequences (2381 bp) and the 5' intergenic region with the Nterminal coding sequence of gH up to a polymorphic BamHI site (427 bp). Infected cell DNA from five laboratory reference strains including GS, Ul102, AJ, Z29 and KF were examined together with DNA from peripheral blood lymphocytes infected with HHV-6 reactivated from blood and/or marrow from five bone marrow transplant (BMT) patients. Separate blood and marrow isolates were obtained from four BMT patients. In addition, HHV-6 sequences were examined directly from one of six Hodgkin's lymphomas and six B cell proliferations which contained HHV-6 DNA as detected by PCR amplification. The results show two groups of very closely related but heterogeneous strains which correlate with previous groupings by antigenic and restriction site differences. These are variant A strains (including laboratory strains GS, Ul102 and AJ) and variant B strains (including laboratory strains Z29 and KF, the Hodgkin's lymphoma strain, and the nine BMT patient isolates). Variations between the groups were 4 to 6 % in nucleotide sequence and 5 to 8.5 % in amino acid sequence. Within each group maximum heterogeneity was observed in different genes. Variant A strains differed by 2-0% in the variable glycoprotein gene sequence whereas variant B strains were identical in this region; conversely, variant B strains differed by 2 to 3 % in the gH N-terminal and intergenic sequences whereas variant A strains differed there by less than 0'2%. There was evidence for sequence drift independent of selection: relationships between the groups were shown by analyses of amino acid sequence, coding nucleotide sequence as well as intergenic sequence, and the B variant-specific BamHI site in the gH gene was due to a non-coding nucleotide substitution. There was little evidence for in vivo or in vitro variation: the gH nucleotide sequence from the uncultured lymphoma strain (first variant B gH gene identified) was almost identical to the gH sequence from four BMT isolates, and matched BMT isolates from blood and marrow were identical or with a single nucleotide substitution. The overall variation observed between the HHV-6 strain groups was similar or less than that seen between human cytomegalovirus strains such as AD169 or Towne, but deafly distinct from the much greater divergence between currently designated herpesvirus species.

Interaction of Glycoprotein H of Human Herpesvirus 6 with the Cellular Receptor CD46

“…Although our experiments were performed only with HHV-6A, the close homology (ϳ95%, Ref. 42) and immunological cross-reactivity (10) between gH of HHV-6 A and B as well as the shared use of CD46 as a receptor by both variants (3) suggest identical involvement of this glycoprotein in the CD46 interaction for both HHV-6 A and B.…”

Divergence and Recombination of Clinical Herpes Simplex Virus Type 2 Isolates

“…The evolutionary relationships among the different herpesviruses infecting humans, reptiles, and other vertebrates, as well as invertebrates, have been described, and the speciation can be traced back 10 million to hundreds of millions of years ago (39). Based on DNA sequence data from clinical isolates, divergence into different genogroups has been described for human herpesviruses HSV-1 (2,47,55), VZV (45,48,50), Epstein-Barr virus (57), cytomegalovirus (7,8), human herpesvirus 6 (HHV-6) (11,20), , and HHV-8 (42). Information regarding the genetic variability of clinical HSV-2 isolates has been limited to date.…”

The R3 Region, One of Three Major Repetitive Regions of Human Herpesvirus 6, Is a Strong Enhancer of Immediate-Early Gene U95

“…HHV-6 predominantly infects and replicates in CD4 ϩ lymphocytes (30,48) and may establish latency in the monocyte/macrophage lineage (26). HHV-6 isolates are segregated into two closely related variants, A (HHV-6A) and B (HHV-6B), based on molecular and biological criteria (1,3,9,18,45,53,54). HHV-6B is the causative agent of exanthem subitum (roseola) (55), a common childhood disease, whereas the pathological role of HHV-6A remains to be determined.…”