The family Herpesviridae: an update. The Herpesvirus Study Group of the International Committee on Taxonomy of Viruses

Genomic organization and evolution of the human herpesviruses

Members of the Herpesviridae family have been isolated from most animal species examined. Of approximately 100 individual virus species, eight have been isolated from humans, and three of these only within the last 10 years. Fortunately, there is now an enormous amount of sequence data from many of these viruses, particularly the eight human herpesviruses. This wealth of sequence information from such a diverse group of related viruses provides a unique resource for studies of viral gene evolution, comparative gene function, and virus identification.

Nested polymerase chain reaction and in situ hybridization for diagnosis of canine herpesvirus infection in puppies

The usefulness of two nucleic acid detection systems in suspected cases of spontaneous canine herpesvirus (CHV) infection in puppies was evaluated. Formalin-fixed, paraffin-embedded tissues from seven 1-3-week-old naturally infected puppies with lesions characteristic of CHV infection were investigated in a retrospective study. Nested polymerase chain reaction (PCR) and nonradioactive in situ hybridization (ISH) were used to detect nucleotide sequences of the CHV thymidine kinase (TK) gene. According to the original necropsy reports, CHV was isolated in four of the seven puppies using primary canine lung and/or kidney cells. In all seven puppies, gross and histologic lesions consisted of disseminated focal necroses and hemorrhages predominantly in kidneys, lung, liver, and spleen. In addition, few small amphophilic intranuclear inclusion bodies were detected by light microscopy mainly in epithelial cells of kidney, lung, and liver. ISH was performed with a 111-base-pair (bp) digoxigenin-labeled double-stranded DNA probe. Viral DNA was detected in the nuclei of cells near and within lesions. Various cell types, including bronchiolar and alveolar epithelial cells, hepatocytes, renal tubular epithelial cells, neurons, fibrocytes, cardiac myocytes, and endothelial cells, were positive for viral DNA. PCR amplification products of the expected length of 168 bp containing the expected cleavage site for the restriction enzyme EcoRI, derived from paraffin blocks containing lung, kidney, and liver tissues, were detected in all seven puppies. The specificity of the obtained amplicon was further confirmed by Southern blot analysis. ISH and PCR are both useful methods for diagnosing CHV infection in formalin-fixed, paraffin-embedded tissues and are highly specific and sensitive methods for further investigations of the pathogenesis of CHV-induced lesions.

Detection of a novel bovine lymphotropic herpesvirus

Degenerate PCR primers which amplify a conserved region of the DNA polymerase genes of the herpesvirus family were used to provide sequence evidence for a new bovine herpesvirus in bovine B-lymphoma cells and peripheral blood mononuclear cells (PBMC). The sequence of the resultant amplicon was found to be distinct from those of known herpesvirus isolates. Alignment of amino acid sequences demonstrated 70% identity with ovine herpesvirus 2, 69% with alcelaphine herpesvirus 1, 65% with bovine herpesvirus 4, and 42% with bovine herpesvirus 1. Phylogenetic analysis placed this putative virus within the tumorigenic Gammaherpesvirinae subfamily, and it is tentatively identified as bovine lymphotropic herpesvirus. This novel agent was expressed in vitro from infected PBMC, and cell-free supernatants were used to transfer infection to a bovine B-cell line, BL3. Analysis, with specific PCR primers, of DNA from bovine PBMC and lymphoma cells identified infection in blood of 91% of adult animals (n = 101), 63% of lymphomas (n = 32), and 38% of juveniles (n = 13). Of the adults, herpesvirus infection was present in 94% of animals that were seropositive for bovine leukemia virus (BLV) (n = 63) and in 87% of BLV-seronegative animals (n = 38). Of the seropositive group, 17 animals exhibited persistent lymphocytosis, and 100% of these were herpesvirus positive by PCR. A role for bovine lymphotropic herpesvirus as a cofactor in BLV pathogenesis is considered.

Mutation of the Lck-binding motif of Tip enhances lymphoid cell activation by herpesvirus saimiri

The proline-rich SH3-binding (SH3B) motif of the tyrosine kinase-interacting protein (Tip) of herpesvirus saimiri (HVS) is required for binding to the cellular Src family kinase Lck. We constructed a mutant form of HVS in which prolines in the SH3B motif of Tip were altered to alanines. This mutant form of Tip was incapable of binding to Lck. The mutant virus, HVS/Tip mSH3B, retained its ability to immortalize common marmoset lymphocytes in culture. In fact, common marmoset lymphocytes immortalized by the HVS/Tip mSH3B mutant displayed increased expression of HLA-DR lymphocyte activation marker, an altered pattern of tyrosine phosphorylation, increased expression of the tyrosine kinase Lyn, and a shift in electrophoretic mobility of Lck compared to cells immortalized by wild-type HVS. Experimental infection of common marmosets resulted in fulminant lymphoma with both HVS/Tip mSH3B and wild-type HVS. However, HVS/Tip mSH3B produced greater infiltration of affected organs by proliferating lymphoid cells compared to wild-type HVS. These results demonstrate that Tip binding to Lck is not necessary for transformation and that abrogation of Tip binding to Lck alters the characteristics of transformed cells and the severity of the pathologic lesions.

PCR studies on the potential sites for latency of BHV-4 in calves

The aim of the study was to examine various tissues of experimentally infected calves for the BHV-4 genome so as to detect in which cells the virus persists during the latent phase of the infection. The presence of the bovine herpesvirus type 4 genome was detected by a nested PCR in a variety of tissues collected from two susceptible calves experimentally infected 62 days earlier. Mild clinical signs of bronchitis, an elevated body temperature for 2-3 days, and a slightly increased number of blood leukocytes were observed in both inoculated calves. BHV-4 was demonstrated in seven samples from the 12 different parts of the nervous system tested from each calf (29.1%), from the cornea, from lymph nodes near to the inoculation site, from the gallbladder and from the bone marrow. Thus a member of the predominantly lymphotropic Gammaherpesvirinae subfamily was detected in neural tissue and other organs that have never been associated with persistence.

Pseudorabies virus glycoprotein gK is a virion structural component involved in virus release but is not required for entry

The pseudorabies virus (PrV) gene homologous to herpes simplex virus type 1 (HSV-1) UL53, which encodes HSV-1 glycoprotein K (gK), has recently been sequenced (J. Baumeister, B. G. Klupp, and T. C. Mettenleiter, J. Virol. 69:5560-5567, 1995). To identify the corresponding protein, a rabbit antiserum was raised against a 40-kDa glutathione S-transferase-gK fusion protein expressed in Escherichia coli. In Western blot analysis, this serum detected a 32-kDa polypeptide in PrV-infected cell lysates as well as a 36-kDa protein in purified virion preparations, demonstrating that PrV gK is a structural component of virions. After treatment of purified virions with endoglycosidase H, a 34-kDa protein was detected, while after incubation with N-glycosidase F, a 32-kDa protein was specifically recognized. This finding indicates that virion gK is modified by N-linked glycans of complex as well as high-mannose type. For functional analysis, the UL53 open reading frame was interrupted after codon 164 by insertion of a gG-lacZ expression cassette into the wild-type PrV genome (PrV-gKbeta) or by insertion of the bovine herpesvirus 1 gB gene into a PrV gB- genome (PrV-gK(gB)). Infectious mutant virus progeny was obtained only on complementing gK-expressing cells, suggesting that gK has an important function in the replication cycle. After infection of Vero cells with either gK mutant, only single infected cells or small foci of infected cells were visible. In addition, virus yield was reduced approximately 30-fold, and penetration kinetics showed a delay in entry which could be compensated for by phenotypic gK complementation. Interestingly, the plating efficiency of PrV-gKbeta was similar to that of wild-type PrV on complementing and noncomplementing cells, pointing to an essential function of gK in virus egress but not entry. Ultrastructurally, virus assembly and morphogenesis of PrV gK mutants in noncomplementing cells were similar to wild-type virus. However, late in infection, numerous nucleocapsids were found directly underneath the plasma membrane in stages typical for the entry process, a phenomenon not observed after wild-type virus infection and also not visible after infection of gK-complementing cells. Thus, we postulate that presence of gK is important to inhibit immediate reinfection.

Transmission of ovine herpesvirus 2 in lambs

The pattern of acquisition of ovine herpesvirus 2 (OHV-2) infection in lambs was examined by a competitive-inhibition enzyme-linked immunosorbent assay and PCR. Newborn lambs (n = 118) did not exhibit antibody at birth. Viral DNA in peripheral blood leukocytes was detected in only 3% (n = 77) of newborn lambs before suckling. After nursing, viral DNA was sporadically present in about 10 to 20% of lambs until about 3 months of age. Thereafter, strong DNA signals began to appear in increasing numbers of lambs, reaching 100% by 5.5 months of age. Viral DNA in nasal secretions began to be detectable in about 30% of lambs at 5.5 months of age, achieved significant levels in 88% of lambs by 7.5 months of age, and then declined. The kinetics of the humoral immune response in lambs paralleled those of viral DNA in nasal secretions but did not parallel its presence in blood leukocytes. In the experiment to define the time of infection of OHV-2 in lambs, all five lambs separated from the flock at 2.5 months of age remained uninfected until the termination of the experiment at 1 year of age. In contrast, lambs weaned at 2.5 months of age and returned to the flock had become infected at 3.5 months of age. Weaning and separation from the flock at 3.5 months of age did not prevent infection. The study showed that OHV-2 infection does not commonly occur in perinatal lambs and that OHV-2-free sheep can be established by separation of lambs at the proper time, which has important implications for potential control measures.

Gene arrangement within the unique long genome region of infectious laryngotracheitis virus is distinct from that of other alphaherpesviruses

The genome of the avian alphaherpesvirus infectious laryngotracheitis virus (ILTV) comprises ca. 155 kbp of which ca. one-third have been sequenced so far. To gain additional sequence information we analyzed two stretches of 15.5 and 1.9 kbp of the ILTV unique long (U(L)) genome region. The larger fragment contains homologs of the herpes simplex virus (HSV) UL23 (thymidine kinase) and UL22 (glycoprotein H) genes followed by five open reading frames (ORF) encoding putative proteins of 334 to 410 amino acids which exhibit no homology to any known herpesvirus protein. RNA analyses showed that these unique ILTV genes are indeed expressed. An origin of replication separates this cluster of unique genes from a conserved gene cluster consisting of the UL45, UL46, UL48, UL49, UL49.5, and UL50 homologs. The absence of UL47 from this position coincides with the localization of a UL47-homologous ORF within the unique short (U(S)) region of the ILTV genome (M. Wild, S. Cook, and M. Cochran, Virus Genes 12:107-116, 1996). Within the second analyzed region the ILTV UL21 homolog was found adjacent to the UL44 gene. We thus identified five novel herpesvirus genes in ILTV and present evidence for a large internal inversion in the ILTV U(L) region, in contrast to the collinear genomes of other alphaherpesviruses. Interestingly, a similar inversion is also present in the porcine alphaherpesvirus pseudorabies virus.

The Scope of Viral Vectors for the Transduction of Haemopoietic Cells

Over the last five years significant progress has been made towards the transfer of foreign genetic material to eukaryotic cells. The eventual aim to devise novel therapeutic strategies to treat human diseases, in particular solid tumours and monogenic disorders associated with various enzyme deficiency states. The easy accessibility and the ability of haemopoetic stem cells to self replicate and repopulate makes them desirable targets for gene transfer. In theory the introduction of a small number of gene modifed haemopoetic progenitor cells can allow therapy of an individual for life without any further intervention. This approach has been used for the treatment of single gene defects such as ADA deficiency. Furthermore, gene transfer technology has increasingly been exploited for bone marrow and peripheral blood stem cell marking studies, modification of cell sensitivity to cytotoxic drugs and the genetic modification of leukemic cells with the intention of inducing a leukemia specific cytotoxic T cell response. Vector development is of crucial importance for the successful delivery of genes in haemopoetic stem cells and leukemia cells. The objective of this review is to discuss in detail the properties of current vector technology that are pertinent to haemopoietic cell gene transduction.

A herpesvirus of rhesus monkeys related to the human Kaposi's sarcoma-associated herpesvirus

A herpesvirus that is related to but distinct from the Kaposi's sarcoma-associated herpesvirus (KSHV, or human herpesvirus 8) was isolated from rhesus monkeys. The sequence of 10.6 kbp from virion DNA revealed the presence of an interleukin-6 homolog similar to what is present in KSHV and a closer relatedness of the DNA polymerase and glycoprotein B reading frames to those of KSHV than to those of any other herpesvirus. This rhesus monkey herpesvirus replicated lytically and to high titers in cultured rhesus monkey fibroblasts. Antibody testing revealed a high prevalence for at least 10 years in our rhesus monkey colony and a high prevalence in two other colonies that were tested. Thus, rhesus monkeys naturally harbor a virus related to KSHV, which we have called RRV, for rhesus monkey rhadinovirus.

Herpesvirus of turkeys homologue of HSV VP16 is structurally related to varicella zoster virus trans-inducing protein encoded by ORF 10

Expression of the immediate-early genes of alpha-herpesviruses is stimulated by a family of trans-inducing factors represented by VP16 of HSV-1 and ORF10 gene product of VZV. We have identified and determined the nucleotide sequence of the UL48 gene encoding the herpesvirus of turkeys (HVT) homologue of HSV VP16. The gene maps to the BamHI-J fragment and appears to be expressed in a form of bicistronic transcript together with UL49. The deduced amino acid sequence of the protein encoded by HVT UL48 gene shows 55% identity with MDV UL48 gene product. Like the majority of related proteins in other alpha-herpesviruses, the protein encoded by HVT UL48 gene lacks the acidic C-terminal tail, known to possess the transactivation capacity of HSV VP16. Hydrophobic cluster analysis has revealed that its predicted domain composition is closely related to the transactivator protein encoded by ORF10 of VZV. However, the putative amino-terminal activation domain of the HVT homologue of HSV VP16 does not contain a typical horseshoe-like hydrophobic cluster found in other alpha-herpesvirus homologues, suggesting either that it acts as a transactivator via a different activation domain or that its transactivation potential is diminished.

Establishment and characterization of porcine cytolytic cell lines and clones

Although non-major-histocompatibility-complex-restricted cytolytic cells appear to significantly influence antiviral immunity in pigs, the phenotype and functional characteristics of these cells are not well defined. To allow a detailed analysis of these subsets, we established and characterized cell lines and clones of interleukin-2-activated (IL-2) cytolytic cells. Cell lines and clones were obtained from peripheral blood mononuclear cells of minipigs of the swine-leucocyte-antigen-complex (SLA) d/d haplotype. Cells were cultured in the presence of human recombinant IL-2 and cloned by double limiting dilution in the presence of gamma-irradiated L14 cells (a retrovirus immortalized B-lymphoblastoid cell line of the haplotype SLAd/d) or gamma-irradiated autologous peripheral blood mononuclear cells as feeder cells. Cytolytic cell lines and clones were characterized for their ability to kill different target cells and for their cell surface phenotype. All obtained clones expressed CD2 and CD8 and were negative for CD4. The following three subsets of cytolytic cells were identified: Subset 1) CD3- CD5- cells that killed K562 cells (a natural killer cell susceptible target cell line), as well as the pseudorabies virus (PRV)-infected or uninfected porcine kidney cells. These cells were considered to be typical natural killer cells. Subset 2) CD3 gamma/delta + CD5- T-cells that killed K562 cells and PRV virus-infected or uninfected porcine kidney cells, infected or uninfected L14 cells, and L14 cells constitutively expressing the PRV viral glycoprotein gB or gC. These cells were considered to be gamma/delta T-cells with natural killer activity. Subset 3) CD3 alpha/beta + CD5+ T-cells that killed L14 cells, PRV-infected L14 cells, and PRV gB- and gC-transfected L14 cells. These cells were possibly induced by the L14 feeder cells, used in the in vitro culture system. None of the cytolytic effector cells killed only MHC-matched viral infected cells. In conclusion, we describe a method to isolate, clone, and culture cytolytic cells from pigs. The clones could be cultured for 5 months, which allowed appropriate phenotypic and functional characterization of the various clones. Two of the subsets, CD3 gamma/delta T- and the natural killer cell subset may be involved in antiviral immunity in this species.

Specific detection of shedding and latency of bovine herpesvirus 1 and 5 using a nested polymerase chain reaction

A sensitive method for simultaneously detecting and discriminating between bovine herpesviruses types 1 and 5 (BHV-1 and BHV-5) was developed using a nested polymerase chain reaction (PCR) technique. Following amplification using type-common primers derived from gC sequences, amplification using type-specific nesting primers produced different-sized bands specific to the corresponding types, as demonstrated by blot hybridization. Less than 0.1 plaque-forming units (PFU) of each virus and 75 fg or less of viral DNA were routinely detected. The PCR technique amplified correct product from 4 BHV-5 isolates and from 48 BHV-1 isolates, all from the United States, and did not amplify heterologous herpesviruses. The PCR technique was more sensitive than virus isolation in detection of BHV-1 or BHV-5 in nasal secretions from experimentally and naturally infected calves, and it detected BHV-1 or BHV-5 in trigeminal ganglia from these calves.

Molecular and clinicopathological diagnosis of malignant catarrhal fever in cattle, deer and buffalo in New Zealand

Fresh and formalin-fixed tissues and blood samples in ethylenediaminetetraacetate were collected from cattle, deer and buffalo with clinical signs suggestive of malignant catarrhal fever (MCF). In addition, formalin-fixed, paraffin-embedded tissue blocks collected from these animals and retrospectively from field cases of MCF were examined. DNA samples extracted from these samples were analysed by polymerase chain reaction (PCR) assay using primers specific for the sheep-associated (SA)- and wildebeest-associated (WA)-MCF viruses. Both the SA-MCF virus and WA-MCF virus PCR yielded positive results which were in nearly complete agreement with the histopathological diagnoses of MCF in fresh and formalin-fixed, paraffin-embedded tissue from 29 cattle, 24 deer and three buffaloes. Some blood samples tested by the two assays indicated that some of the infected cattle were possible carriers.

Analysis of bovine herpesvirus 1 transcripts during a primary infection of trigeminal ganglia of cattle

During an infection of nonneuronal cells, bovine herpesvirus 1 (BHV-1) gene expression proceeds in a well-defined cascade. Products of immediate-early (IE) genes are expressed first, and they activate expression of early (E) and late (L) genes. Although the same cascade is assumed to occur during an infection of neurons in trigeminal ganglia (TG) of cattle, no experimental data is available to support this hypothesis. Consequently, we analyzed BHV-1 gene expression in bovine TG at 1, 2, 4, 7, and 15 days postinfection (dpi). Infectious virus was detected in ocular swabs from 1 to 7 dpi but not 15 dpi. By reverse transcription (RT)-PCR, IE (bICP4), E (thymidine kinase, ribonucleotide reductase [RR]), L (glycoprotein C, and alpha trans-inducing factor), and dual-kinetic (bICP0 and bICP22) transcripts were analyzed. When cDNA synthesis was primed with random hexamers, IE and E transcripts were detected at the same time. However, full-length and poly(A)+ (FL&P) RR or bICP22 RNAs were detected before FL&P IE RNAs. Furthermore, FL&P IE transcripts were not detected until viral DNA increased in TG. IE transcripts were detected before E or L RNAs when rabbit kidney cells were infected with a low multiplicity of infection and the same RT-PCR detection method was used. These studies suggested that expression of full-length and polyadenylated IE transcripts in trigeminal ganglia was not efficient compared to that of RR and bICP22 transcripts.

Histological studies of bovine herpesvirus type 4 infection in non-ruminant species

The pathology of bovine herpesvirus type 4 (BHV-4) infection was studied in cats, rabbits and guinea pigs. Twenty kittens, twenty-two rabbits and ten guinea pigs, some treated with glucocorticoid-were inoculated with a BHV-4 strain of feline origin, via various routes of inoculation (conjunctival, intranasal, peritoneal). Clinical signs were recorded. After euthanizing at different post inoculation days macro- and microscopic changes were observed by necropsy and in hematoxylin-eosin stained histological sections. The presence of the virus in organs was detected by immunohistochemistry and a nested PCR assay. Inclusion bodies and monoclonal antibody-stained cells were found in the conjunctiva, trachea, lungs, spleen and lymph nodes. Most of the lesions were localized to the respiratory and the immune system. The macro- and microscopic lesions and clinical signs were more severe in kittens and guinea pigs. The histological data indicated that cats, especially kittens, were susceptible for BHV-4 and the infection was not confined to the urinary bladder.

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.

Ultrastructural characterization of human herpesvirus 8 (Kaposi's sarcoma-associated herpesvirus) in Kaposi's sarcoma lesions: electron microscopy permits distinction from cytomegalovirus (CMV)

Kaposi's sarcoma (KS) has been shown by molecular techniques to be associated with infection with human herpesvirus 8 (HHV8/KSHV), but specific ultrastructural characterization of the virus has been impaired by the frequent presence in these lesions of other herpesviruses, particularly cytomegalovirus (CMV). Since the ultrastructural appearance of HHV8/KSHV has been studied in the cell line KS-1 uninfected with other viruses including CMV, it was possible to undertake a comparative study of CMV and HHV8/KSHV in KS lesions. HHV8/KSHV was sparsely present and lytic infection was restricted to endothelial cells. The following specific ultrastructural features allowed distinction between HHV8/KSHV and CMV: the viral particles were more delicate and less numerous in cases of HHV8/KSHV infection; the viral tegument was more electron-dense in CMV than in HHV8/KSHV; dense bodies characteristic of CMV were absent in HHV/KSHV; complete CMV viral particles were more variable in size and generally larger (150-200 nm) than HHV8/KSHV (120-150 nm); and finally, the viral envelope was more pleomorphic in CMV than in KSHV/HHV8. Similarities between CMV and HHV8/KSHV included the basic structure of the nucleocapsids and the presence of capsids lacking central DNA cores (so-called non-infectious enveloped particles). These observations show that electron microscopy can be used to identify HHV8/KSHV and confirm the relationship between HHV8/KSHV and KS.

The pseudorabies virus UL51 gene product is a 30-kilodalton virion component

Positional homologs to the UL51 open reading frame of herpes simplex virus type 1 have been identified throughout the herpesvirus family. However, no respective protein has so far been described for any of the herpesviruses. With rabbit antisera directed against oligopeptides predicted to comprise antigenic regions of the deduced pseudorabies virus (PrV) UL51 protein, a polypeptide with a size of 30 kDa was identified in PrV-infected cell lysates and in purified virions. This molecular mass correlates reasonably well with the predicted mass of 25 kDa of the 236-amino-acid deduced UL51 protein. Antisera raised against peptides derived from different predicted antigenic regions all detected the 30-kDa protein in Western blot (immunoblot) analyses. Specificity was ascertained by peptide competition. Subcellular fractionation showed the presence of the UL51 protein mainly in the nucleus of infected cells. After separation of purified virion preparations into envelope and capsid, the PrV UL51 protein was detected in the capsid fraction. In summary, we identified the first herpesvirus UL51 protein and demonstrate that it represents a structural component of PrV virions.

The UL20 gene product of pseudorabies virus functions in virus egress

The UL20 open reading frame is positionally conserved in different alphaherpesvirus genomes and is predicted to encode an integral membrane protein. A previously described UL20- mutant of herpes simplex virus type 1 (HSV-1) exhibited a defect in egress correlating with retention of virions in the perinuclear space (J. D. Baines, P. L. Ward, G. Campadelli-Fiume, and B. Roizman, J. Virol. 65:6414-6424, 1991). To analyze UL20 function in a related but different herpesvirus, we constructed a UL20- pseudorabies virus (PrV) mutant by insertional mutagenesis. Similar to HSV-1, UL20- PrV was found to be severely impaired in both cell-to-cell spread and release from cultured cells. The severity of this defect appeared to be cell type dependent, being more prominent in Vero than in human 143TK- cells. Surprisingly, electron microscopy revealed the retention of enveloped virus particles in cytoplasmic vesicles of Vero cells infected with UL20- PrV. This contrasts with the situation in the UL20- HSV-1 mutant, which accumulated virions in the perinuclear cisterna of Vero cells. Therefore, the UL20 gene products of PrV and HSV-1 appear to be involved in distinct steps of viral egress, acting in different intracellular compartments. This might be caused either by different functions of the UL20 proteins themselves or by generally different egress pathways of PrV and HSV-1 mediated by other viral gene products.

Bovine herpesvirus 1-induced apoptosis occurs at the G0/G1 phase of the cell cycle

We have previously shown that bovine herpesvirus 1 (BHV-1), even when inactivated, induces apoptotic cell death in mitogen-stimulated bovine peripheral blood mononuclear cells (PBMCs) (Hanon et al., 1996, J. Virol. 70, 4116-4120). In order to gain insight into this process, we have investigated the cell cycle phase at which BHV-1 induces apoptosis in PBMCs. Our results show that the percentage of cells that progress through the S phase was always lower in BHV-1-infected PBMCs than in control cells. This effect was not due to a defective activation of mitogen-stimulated PBMCs since BHV-1 only slightly affected the percentage of cells expressing BoCD25, a well-known lymphocyte activation marker. Furthermore, mimosine and cyclosporine A, two chemicals that inhibit entry into the S phase of the cell cycle by different pathways, did not affect the ability of BHV-1 to induce apoptosis. BHV-1-induced apoptosis also occurred in unstimulated PBMCs and interestingly, this was associated with the expression of c-myc and BoCD25 proteins both of which are related to cell cycle progression. All together, these data provide evidence demonstrating that BHV-1-induced apoptosis occurs at the G0/G1 phase of the cell cycle.

Detection of latency-associated transcripts of equid herpesvirus 1 in equine leukocytes but not in trigeminal ganglia

Results from Southern hybridization and PCR amplification experiments using a randomly synthesized reverse transcription-PCR product showed that peripheral blood leukocytes from horses showing no clinical signs of disease expressed a putative latency-associated transcript antisense to and overlapping the 3' end of the equid herpesvirus 1 (EHV-1) immediate-early gene (gene 64). A PCR product derived from this transcript has > or =96% identity with the published EHV-1 sequence. In situ hybridization studies of equine bronchial lymph nodes corroborated these findings and are consistent with reactivation data (D. A. Smith, A. Hamblin, and N. Edington, unpublished data), indicating that EHV-1 latency is established predominantly in CD5+/CD8+ leukocytes.

An equine herpesvirus-1 gene 71 deletant is attenuated and elicits a protective immune response in mice

The pathogenesis of pulmonary infection and the immune response following intranasal inoculation of mice with two equine herpesvirus type 1 (EHV-1) deletion mutants have been assessed. The mutants, ED71 and ED75, have deletions in genes 71 (EUS4) and 75 (10K), respectively. Deletions were replaced by the Escherichia coli lacZ gene driven by the simian virus 40 (SV40) early promoter. It has previously been shown that the protein products of genes 71 and 75 are dispensable in vitro but that removal of gene 71 results in a defect in virus maturation and capsid envelopment which impairs the ability of mutant virus to spread via release and readsorption. This study demonstrated that the 192-kDa gene 71 product is required for full expression of virulence in mice, whereas the putative 10-kDa product of gene 75 has minimal effect. Both mutants exhibited the same tissue and cytotropism as wild-type EHV-1 and induced both humoral and cell-mediated immune responses indistinguishable from those induced by the parental strain. Irrespective of the reduced pathogenicity of the gene 71 mutant, infected mice were protected against a challenge with wild-type EHV-1. These findings highlight the potential of ED71 as a vaccine candidate.

Generation of herpes virus saimiri-transformed T-cell lines from macaques is restricted by reactivation of simian spuma viruses

Herpes virus saimiri (HVS) transforms human T-cells in vitro to stable growth. These T-cell lines retain their immunological characteristics of the parent cells and do not release infectious virus. Recently, lymphocytes of Old World monkeys were efficiently transformed by HVS. In parallel to these studies we initiated transformation experiments by infecting peripheral blood cell cultures of 45 monkeys, 35 rhesus and 10 cynomolgus macaques. In only three cases, we obtained transformed T-cell lines. The transformed T-cells were largely double-positive for CD4 and CD8. They responded with increased proliferation to mitogenic or IL-2 stimulation and transcribed mRNA for IL-2, IL-4, and IL-10. However, most initiated T-cell cultures from macaques developed giant cells. The cytopathic agent was identified as simian foamy virus (SFV) as confirmed by PCR, immunofluorescence, and coculture experiments. Treatment of the T-cell cultures with AZT- and SFV-specific sera did only shortly prolong the life-span of the cultures. Therefore, the reactivation of SFV caused remarkable difficulties in the establishment of macaque T-cell lines by HVS. This seems to be a general problem since most animals from several breeding colonies are SFV-positive.

DIFERENCIAÇÃO ENTRE OS VÍRUS DA RINOTRAQUEÍTE INFECCIOSA BOVINA (BHV-1) E HERPESVÍRUS DA ENCEFALITE BOVINA (BHV-5) COM ANTICORPOS MONOCLONAIS

Amostras de herpesvírus bovinos (BHV) tipo 1 (Virus da Rinotraqueíte Infecciosa Bovina/Vulvovaginite Pustular Infecciosa; BHV-1) e tipo 5 (Herpesvírus da Encefalite Bovina; BHV-5) tiveram seu perfil de reatividade analisado em testes de imunoperoxidase frente a um painel composto por cinco anticorpos monoclonais (AcM) produzidos contra antígenos de BHV-1. Um dos AcM reconheceu todas as amostras de BHV examinadas. Os quatro AcM restantes reconheceram somente amostras de BHV-1. Todas as amostras isoladas de casos de encefalites (BHV-5) apresentaram um padrão de reação distinto daquelas isoladas de outros síndromes associados à infecção pelo BHV-1. Os resultados obtidos indicam que os AcM avaliados permitem a diferenciação entre amostras de BHV-1 e BHV-5, havendo perfeita correlação entre os quadros clínicos observados com os perfis de reatividade obtidos in vitro.

Human herpesvirus type-8 (HHV-8) in haematopoietic neoplasia

Human herpesvirus type-8 (HHV-8) is a lymphotropic herpesvirus originally identified in Kaposi's sarcoma. Among lymphoproliferative disorders, HHV-8 infection is restricted to body-cavity-based lymphoma (BCBL) and multicentric Castleman's disease (MCD). BCBL are B-cell lymphomas growing in liquid phase in the body cavities and most frequently associated with AIDS. BCBL express indeterminate phenotypes, in all cases are associated with HHV-8 infection, and frequently carry Epstein-Barr virus genomes in the absence of c-MYC rearrangements or other genetic lesions characteristic of B-cell lymphomas. The clinical outcome of BCBL is poor with a median survival of only few months. MCD is an atypical lymphoproliferative disorder which displays marked vascular hyperplasia and is commonly associated with Kaposi's sarcoma. HHV-8 infection occurs in 100% of AIDS-related MCD and in approximately 40% of AIDS-unrelated cases. Overall, the consistency of HHV-8 infection in BCBL and MCD, its selectivity throughout the spectrum of lymphoproliferative disorders and the high copy number of HHV-8 DNA sequences in infected cells suggest that the virus plays a pathogenetic role in these disorders.

A contribution to the systematization of bovine herpesvirus 1 based on genomic mapping by restriction fragment pattern analysis

Fourteen isolates of bovine herpesvirus 1 (BHV-1) found representative of more than 100 isolates studied, were compared by restriction fragment pattern analyses and molecularly characterized. A number of evolutionary links between the variants originally associated with infectious bovine rhinotracheitis and the variants originally associated with infectious pustular vulvovaginitis were identified. These findings, as well as the lack of any correlation between genome type and clinical manifestation, confirm that there is no phylogenetic basis for a distinction between groups of strains associated with genital and respiratory disease. Two attenuated vaccine strains can be identified as deviating from field isolates.

Characterization of canine herpesvirus glycoprotein C expressed by a recombinant baculovirus in insect cells

The gene encoding the canine herpesvirus (CHV) glycoprotein C (gC) homologue has been identified by sequence homology analyses with other well studied herpesviruses. Previously, we have identified three CHV glycoproteins, gp145/112, gp80 and gp47 using a panel of monoclonal antibodies (MAbs). To determine which CHV glycoprotein corresponds to gC, a recombinant baculovirus which contains the putative CHV gC structural gene under the baculovirus polyhedrin promoter was constructed. The recombinant baculovirus expressed gC-related polypeptides (44-62 kDa), which reacted only with MAbs against CHV gp80, indicating that the previously identified CHV gp80 is the translation product of the gC gene. The baculovirus expressed gC was glycosylated and transported to the surface of infected cells. At least seven neutralizing epitopes were conserved on the gC produced in insect cells. It was found that the recombinant baculovirus infected cells adsorbed murine erythrocytes as is the case for CHV-infected cells. The hemadsorption activity was inhibited by heparin, indicating that the CHV gC binds to heparan sulfate on the surface of murine erythrocytes. Mice immunized with the recombinant gC produced strong neutralizing antibodies. Our results suggest that CHV gC produced in insect cells may be useful as a subunit vaccine to control CHV infections.

Detection of canine herpesvirus 1 in a wide range of tissues using the polymerase chain reaction

Canine herpesvirus 1 (CHV-1), a member of the alphaherpesvirus sub-family, is known to cause fatal infections in litters of puppies and may also be involved in infertility, abortion, and stillbirths in adult dogs. The purpose of this study was to determine the presence of CHV-1 DNA using the polymerase chain reaction (PCR) in twelve key sites that have been associated with latency for the other herpesviruses. A 605 base pair portion of the viral glycoprotein B (gB) gene was amplified using degenerate primers, cloned, and sequenced. Conventional 20 mer primers were designed using this sequence information to amplify a 120 bp fragment of gB situated between the original degenerate primers. The specificity of amplification was confirmed by Southern Blot hybridisation using an internal oligonucleotide probe. DNA was extracted from tissue samples taken from twelve dogs at post mortem and from twenty-four blood samples. Nine out of twelve dogs showed evidence of infection with CHV-1; the tissues most commonly affected were lumbo-sacral ganglia (5/12 dogs), tonsil (5/12), parotid salivary gland (4/9), and liver (4/9). No positive results were detected within the twenty-four blood samples. These results indicate that exposure to CHV-1 may be much more common than previously suggested.

Bovine herpesvirus 4: genomic organization and relationship with two other gammaherpesviruses, Epstein-Barr virus and herpesvirus saimiri

Bovine herpesvirus 4 (BHV-4) belongs to the gammaherpesvirinae subfamily. Although the whole sequence of BHV-4 genome is not known it was possible, based on random sequencing, to assume that its genomic organization consists of genes clustered in blocks whose orientation and location in the genome are conserved within a herpesvirus subfamily. Between these blocks lie genes which are specific to either a particular virus or a virus subfamily. BHV-4 genome consists of 5 gene blocks conserved among the gammaherpesviruses and particularly within the Epstein-Barr virus (EBV) and the herpesvirus saimiri (HVS) genomes. Analysis of the regions located outside the gene blocks showed the presence of 12 open reading frames (ORFs). Protein database comparisons showed that no ORF translation products were similar to proteins encoded by alpha- or beta-herpesviruses. Nevertheless, 5 ORFs were homologous in amino acid sequences to proteins encoded by HVS and one was similar to a protein encoded by both HVS and EBV. On the basis of the molecular data BHV-4 is more closely related to HVS than to EBV. Genes homologous to cellular genes have been described in both HVS and EBV genomes. No genes homologous to presently sequenced cellular genes were found among those found in the BHV-4 genome to date.

Glycoprotein E of bovine herpesvirus type 1 is involved in virus transmission by direct cell-to-cell spread

In order to identify the role of the bovine herpesvirus type 1 (BHV-1) glycoprotein E (gE) in the viral infection cycle, we have constructed a BHV-1 gE deletion mutant strain (BHV-1 gE-). This strain was assayed in vitro by comparing its growth kinetics with the wild type strain used as a host of the deletion. Our results indicate that those conditions which prevent the infection by direct adsorption to the cells (presence of a semi-solid medium or presence of neutralizing antibodies in the medium) selectively inhibit the growth of the gE- strain, suggesting that gE plays a central role in the BHV-1 spread by direct cell-to-cell transmission, a major mechanism of the BHV-1 in vivo virulence.

Retroviral insertional activation of the c-myb proto-oncogene in a Marek's disease T-lymphoma cell line

Marek's disease virus (MDV) is an avian herpesvirus that causes, in chickens, a lymphoproliferative disease characterized by malignant transformation of T lymphocytes. The rapid onset of polyclonal tumors indicates the existence of MDV-encoded oncogenic products. However, the molecular basis of MDV-induced lymphoproliferative disease and latency remains largely unclear. Several lines of evidence suggest that MDV and Rous-associated virus (RAV) might cooperate in the development of B-cell lymphomas induced by RAV. Our present results indicate for the first time that MDV and RAV might also act synergistically in the development of T-cell lymphomas. We report an example of an MDV-transformed T-lymphoblastoid cell line (T9) expressing high levels of a truncated C-MYB protein as a result of RAV integration within one c-myb allele. The chimeric RAV-c-myb mRNA species initiated in the 5' long terminal repeat of RAV are deprived of sequences corresponding to c-myb exons 1 to 3. The attenuation of MDV oncogenicity has been strongly related to structural changes in the MDV BamHI-D and BamHI-H DNA fragments. We have established that both DNA restriction fragments are rearranged in the T9 MDV-transformed cells. Our results suggest that retroviral insertional activation of the c-myb proto-oncogene is a critical factor involved in the maintenance of the transformed phenotype and the tumorigenic potential of this T-lymphoma cell line.

Immunobiology of pseudorabies (Aujeszky's disease)

Aujeszky's Disease (AD), a serious illness of pigs causing significant economic losses in the pig industry, is caused by Pseudorabies Virus (PrV). PrV belongs to the alphaherpesvirus subfamily of the herpesviruses with a double-stranded DNA genome in an enveloped capsid capable of encoding approximately 70 proteins. For disease control, vaccination with live and killed vaccines is performed. Recently, 'marked' vaccines have become available for use in eradication programs based on the differentiation between infected and vaccinated animals. PrV is also used as a viral vector for the development of multivalent vaccines. Despite the effectiveness of PrV vaccines, relatively little is known about the immune response against PrV infection. Several viral envelope glycoproteins have been shown to represent targets for antibody responses, and a number of isolated glycoproteins as well as genetically engineered proteins were able to elicit protective immunity. The nature of the cellular immune response is even less defined. Using viral mutants genetically engineered to lack specific antigens, it has been shown that glycoprotein C (gC) acts as a target for cytotoxic T-lymphocytes, and gB, gC, gD, and gH appear to be involved in stimulation of in vitro proliferation of PBMC from immune animals. In addition, gB and gC have been implicated in recognition of infected cells by lymphokine-activated killer (LAK) cells. In summary, the data indicate a prominent role for viral envelope glycoproteins in eliciting humoral and cellular immune responses in the animal host. A complicating factor is the ability of PrV to productively infect cells of the hematopoietic system, which may impair immune responses and might also play a role in persistent or latent infection.

Determination and analysis of the complete nucleotide sequence of human herpesvirus

Human herpesvirus 7 (HHV-7) is a recently isolated betaherpesvirus that is prevalent in the human population, with primary infection usually occurring in early childhood. HHV-7 is related to human herpesvirus 6 (HHV-6) in terms of both biological and, from limited prior DNA sequence analysis, genetic criteria. However, extensive analysis of the HHV-7 genome has not been reported, and the precise phylogenetic relationship of HHV-7 to the other human betaherpesviruses HHV-6 and human cytomegalovirus has not been determined. Here I report on the determination and analysis of the complete DNA sequence of HHV-7 strain JI. The data establish that the close biological relationship of HHV-6 and HHV-7 is reflected at the genetic level, where there is a very high degree of conservation of genetic content and encoded amino acid sequences. The data also delineate loci of divergence between the HHV-6 and HHV-7 genomes, which occur at the genome terminal in the region of the terminal direct-repeat elements and within limited regions of the unique component. Of potential significance with respect to biological and evolutionary divergence of HHV-6 and HHV-7 are notable structural differences in putative transcriptional regulatory genes specified by the direct-repeat and immediate-early region A loci of these viruses and the absence of an equivalent of the HHV-6 adeno-associated virus type 2 rep gene homolog in HHV-7.

Immunocytochemical study of the pathogenesis of Pacheco's parrot disease in budgerigars

Thirty-five budgerigars were infected with the Psittacid herpesvirus 1 (RSL-1 strain, ATCC) to study the pathogenesis of Pacheco's disease. Intramuscular (i.m.) and oral (p.o.) infection routes were used in 21 and 14 animals respectively. Animals were euthanized on days 1, 2, 3, 4, 6 and 8 post-inoculation (p.i.) and complete postmortem examinations and histological studies were performed. The presence of viral antigen in tissues was detected by immunohistochemical techniques using a rabbit polyclonal antibody. In the i.m.-infected birds, lesions were first detected on the third day p.i. and included necrotizing hepatitis and splenitis, both associated to the presence of viral antigen. Necrotic and inflammatory lesions as well as viral antigen were detected in many organs after the fourth day p.i. (oesophagus, crop, pancreas, kidney, adrenal gland, thyroid and parathyroid glands, thymus, ovary and feathers) proving generalization of the disease. Chronology of the infection was similar in the p.o.-infected birds. However, two main differences were observed between the groups: In the p.o. group, viral antigen was first detected in cloacal mucosa (3rd day p.i.), liver and spleen; and viral entry into target cells and dissemination to the rest of the tissues was slower in this group. In addition, detection of viral antigen in feather follicular epithelial cells and in granulosa cells of organ follicles are findings that could be of relevance to the transmission of the virus.

Identification and characterization of pseudorabies virus glycoprotein gM as a nonessential virion component

Sequence analysis within BamHI fragment 3 of the pseudorabies virus (PrV) genome revealed an open reading frame homologous to the UL10 gene of herpes simplex virus. A rabbit antiserum directed against a synthetic oligopeptide representing the carboxy-terminal 18 amino acids of the predicted UL10 product recognized a major 45-kDa protein in lysates of purified Pr virions. In addition, a second protein of 90 kDa which could represent a dimeric form was observed. Enzymatic deglycosylation showed that the PrV UL10 protein is N glycosylated. Therefore, it was designated PrV gM according to its homolog in herpes simplex virus. A PrV mutant lacking ca. 60% of UL10 coding sequences was able to productively replicate on noncomplementing cells, demonstrating that PrV gM is not required for viral replication in cell culture. However, infectivity of the mutant virus was reduced and penetration was delayed, indicating a modulatory role of PrV gM in the initiation of infection.

Malignant catarrhal fever virus. Characterization of a United States isolate and development of diagnostic assays

Malignant catarrhal fever (MCF) is a severe lymphoproliferative disease of certain domestic and wild ruminants. Two distinct but closely related viruses cause clinically indistinguishable syndromes in susceptible ruminant species: wildebeest-associated MCF virus (WA-MCFV) and sheep-associated MCF virus (SA-MCFV). Neither the pathogenesis nor the epidemiology of SA-MCF is understood, primarily because of a lack of adequate detection methods for the etiologic agent or antibody against that agent. Work designed to develop these tests has been under way in our laboratory. To obtain basic information about the virus, the in vitro growth properties of a US isolate of MCF virus were studied and its major viral proteins identified and characterized by a panel of monoclonal antibodies generated against the isolate. A monoclonal antibody to a broadly conserved epitope of MCF virus was identified, and a competitive-inhibition ELISA (CI-ELISA) was developed for detection of anti-MCF antibody in sheep and other ruminants. The monoclonal antibody (15-A) reacted with an epitope located on a glycoprotein complex, which was present in all isolates of MCF virus examined. Antibody from a wide variety of ruminants infected with MCF virus of both sheep and wildebeest origin competed with the monoclonal antibody 15-A for the epitope, which was not present on 14 other common ruminant viruses. The assay detected antibody in inapparently infected sheep, and in cattle, deer, and bison with clinical MCF. A PCR assay for DNA of the sheep-associated virus was developed, based on previously reported primers. Comparative studies demonstrated that the CI-ELISA was specific for MCFV antibody and that the PCR was more reliable for diagnosis of clinical MCF.

Establishment of a rabbit model for bovine herpesvirus type 5 neurological acute infection

This study was conducted to evaluate the suitability of the rabbit as a model for bovine, herpesvirus 5 (BHV-5) acute infection. In a preliminary experiment, a total of 24 one-month old New Zealand white rabbits were inoculated with BHV-5 or bovine herpesvirus 1 (BHV-1) by the intraconjunctival, intracerebral or intranasal routes. BHV-5 or BHV-1 inoculated in the conjunctiva induced virus proliferation in the eye mucosae and the nasal cavity of rabbits without meningo-encephalitis. On the other hand, only BHV-5 infection by intranasal or intracerebral routes produced a fatal meningo-encephalitis. The intranasal route was used in a further experiment for the establishment of a rabbit model for BHV-5 infection. A total of 45 rabbits were inoculated intranasally with BHV-5 or BHV-1. The results showed that intranasal inoculation of BHV-5 strain N569 in rabbits was followed by the development of a lethal meningo-encephalitis for 66% of rabbits while all BHV-1 infected rabbits remained healthy throughout this experiment (28 days). Analysis between the mortalities of rabbits infected with BHV-5 and BHV-1 were highly significant (p < 0.001). The presence of BHV-5 in the central nervous system (CNS) was confirmed by virus isolation (essentially the cerebrum, midbrain and pons) and by immunohistochemical staining of BHV-5 antigen (essentially in the neurons of the cerebrum) only in BHV-5 infected rabbits showing clinical signs of meningo-encephalitis. The findings obtained confirmed the suitability of a rabbit model for the establishment of BHV-5 neurological acute infection and also as a valuable tool for the comparative study of BHV-5 and BHV-1 neuropathogenicity.

Inactivated bovine herpesvirus 1 induces apoptotic cell death of mitogen-stimulated bovine peripheral blood mononuclear cells

Bovine herpesvirus 1 (BHV-1) is able to inhibit the proliferation of bovine peripheral blood mononuclear cells. Here, we have demonstrated that live BHV-1 and, interestingly, inactivated BHV-1 can induce apoptosis of mitogen-stimulated bovine peripheral blood mononuclear cells in vitro.

Identification and characterization of the pseudorabies virus UL3.5 protein, which is involved in virus egress

Alphaherpesvirus genomes exhibit a generally collinear gene arrangement, and most of their genes are conserved among the different members of the subfamily. Among the exceptions is the UL3.5 gene of pseudorabies virus (PrV) for which positional homologs have been detected in the genomes of varicella-zoster virus, equine herpesvirus 1, and bovine herpesvirus 1 but not in the genomes of herpes simplex virus types 1 and 2. To identify and characterize the predicted 224 amino acid UL3.5 protein of PrV, a rabbit antiserum was prepared against a UL3.5 fusion protein expressed in Escherichia coli. In Western blot (immunoblot) analyses the antiserum detected a 30-kDa protein in the cytoplasm of PrV infected cells which was absent from purified virions. For functional analysis, UL3.5-expressing cell lines were established and virus mutants were isolated after the rescue of defective, glycoprotein B-negative PrV by insertion of the complementing glycoprotein B-encoding gene of bovine herpesvirus 1 at two sites within the UL3.5 locus. A PrV mutant carrying the insertion at codon 159 and expressing a truncated UL3.5 protein was still capable of efficient productive replication in noncomplementing cells. In contrast, a PrV mutant carrying the insertion at codon 10 of the UL3.5 gene did not express detectable UL3.5 protein and exhibited a dramatic growth deficiency on non-complementing cells with regard to plaque formation and one-step replication. Electron microscopical studies showed an accumulation of unenveloped capsids in the vicinity of the Golgi apparatus. This defect could be compensated by propagation on complementing UL3.5-expressing cell lines. Our results thus demonstrate that the PrV UL3.5 gene encodes a nonstructural protein which plays an important role in virus replication, presumably during virus egress. The functionally relevant domains appear to be located within the N-terminal part of the UL3.5 protein which also comprises the region exhibiting the highest level of homology between the predicted UL3.5 homologous proteins of other alphaherpesviruses.

Studies of in vivo distribution of bovine herpesvirus type 4 in the natural host

The in vivo distribution of bovine herpesvirus type 4 (BHV-4) was examined by testing nasal and conjunctival exudates, peripheral blood leukocytes, and various organs of experimentally infected calves. For virus detection, a nested PCR assay, virus isolation, and immunohistochemistry were applied. The nervous system and the muscles were free of viral DNA. Liver and intestinal lymph nodes contained low amounts of virus (less than two copies per 1 microgram of cellular DNA). Intestinal, tonsil, thymus, and kidney tissues contained more viral DNA copies (5 to 50 copies per 1 microgram of cellular DNA). The highest amounts of BHV-4 DNA (50 to 500 copies per 1 microgram of cellular DNA) were found in the spleen, lungs, trachea, and nasal epithelium. Amplification of DNA from blood lymphocytes through postinoculation (p.i.) day 48 proved that the virus started to replicate in these cells immediately after inoculation of the calves and that intensive virus growth took place during the 7 to 8 weeks of the infection. The number of virus-infected lymphocytes reached the maximum on p.i. days 22 to 26 and slowly declined thereafter. Virus-infected cells were found only in the spleen on p.i. day 48 by immunohistochemistry. Western blotting (immunoblotting) detected signs of an immune response against 9 of the 29 BHV-4 proteins.

Equine gammaherpesvirus 2 (EHV2) is latent in B lymphocytes

Peripheral blood leukocytes were collected from 5 Thoroughbred horses and examined for the presence of EHV2 in sub-populations of mononuclear cells. Peripheral blood mononuclear cells were separated on Percoll gradients and then enriched for plastic adherent cells (predominantly monocytes), surface immunoglobulin positive (sIg+) B lymphocytes and T lymphocytes, using panning techniques. The purity of each cell population was assessed by fluorescence activated cell scanning. In an infectious centre assay, each cell population was inoculated onto equine foetal kidney monolayer cell cultures which are fully permissive for the replication of EHV2. Only enrichment for sIg+ B lymphocytes resulted in a marked increase in the number of infectious centres, indicating that EHV2 is present in B lymphocytes. Freeze-thawing of sIg+ B lymphocytes, prior to inoculation onto EFK monolayer cell cultures, resulted in the complete abrogation of infectious centre formation, confirming that EHV2 is latent in B lymphocytes i.e., infectious free virus was not present in the cells. The number of EHV2 infected B lymphocytes varied considerably between horses from 4 to 780 per 10(6) cells. Evidence was also obtained that direct cell to cell contact between the epithelial cells and sIg+ B lymphocytes was necessary for the production of infectious centres. The data indicate that EHV2, like other members of the Gammaherpesvirinae, is latent within B lymphocytes.

Lack of virulence of the murine fibroblast adapted strain, Kentucky A (KyA), of equine herpesvirus type 1 (EHV-1) in young horses

The virulence of the cell culture adapted KyA strain of equine herpesvirus type 1 (EHV-1), which lacks at least six genes by deletions in its genome, was assessed by intranasal inoculation of six young horses that were serologically negative for EHV-1. No horses showed clinical signs, and a neutralizing antibody response against EHV-1 was detected in two horses which had antibodies against EHV-4 prior to the inoculation. A challenge experiment using a highly virulent strain of EHV-1 conducted 4 weeks later against 4 of the 6 horses inoculated intranasally with the KyA strain and 2 control horses revealed that (i) the KyA inoculated horses were protected from manifestation of clinical signs detected in both control horses, with the exception of pyrexia, (ii) duration of virus isolation from the KyA inoculated horses after the challenge was remarkably shortened as compared to that from control horses; (iii) thus, animals inoculated with the KyA and challenged with pathogenic EHV-1 showed a reduction in the time of virus shedding and viremia; (iv) two horses which exhibited no antibody responses after the KyA inoculation showed antibody responses after the challenge significantly higher than those of control horses. The results reveal that the KyA strain has no virulence but still possesses immunogenicity for horses, suggesting that some of the genes deleted from the KyA strain might have importance in the expression of EHV-1 virulence.

A genomic map of infectious laryngotracheitis virus and the sequence and organization of genes present in the unique short and flanking regions

We present a genomic map of infectious laryngotracheitis virus (ILT) and an 18,912 bp sequence containing the entire unique short region and a portion of the flanking short repeats. In determining the genomic map, an 856 bp region repeated as many as 13 times was identified within the short repeats. The unique short sequence contains nine potential open reading frames (ORFs). Six of these ORFs show homology to other known herpesvirus unique short genes. Using the herpes simplex virus nomenclature, these genes are the US2, protein kinase, and glycoproteins G, D, I, and E (ORF 1, 2, 4, 6, 7, and 8, respectively). Interestingly, an open reading frame with homology to HSV-1 UL47 (ORF 3) is found in the unique short. One very large open reading frame (ORF 5) is present and contains a threonine-rich, degenerate repeat sequence. This gene appears to be unique to ILT among sequenced herpesviruses. Two ORFs were identified within the short repeat (SR) region. SRORF 1 is homologous to a gene (SORF3) found in the unique short region in both MDV and HVT, and appears to be specific to avian herpesviruses. SRORF 2 has homology to HSV US10.

Prediction of potential cytotoxic T lymphocyte epitopes of bovine herpesvirus 1 based on allele-specific peptide motifs and proteolytic cleavage specificities

Major histocompatibility complex (MHC) class I molecules present endogenous peptides to cytotoxic T lymphocytes (CTLs). Elucidation of CTL epitopes of intracellular pathogens helps in designing better vaccines to control economically important human and animal diseases. In this study, candidate epitopes that are potentially available for presentation to the CTLs via five bovine MHC class I molecules have been identified. This was accomplished by using the computer programs "Find-patterns" and "Peptidestructure" of GCG package and applying the information on cleavage patterns of cytosolic and endoplasmic reticulum proteases and peptidases as well as MHC class I allele-specific peptide motifs on 23 bovine herpesvirus-1 (BHV-1) proteins available on protein sequence database. Several candidate peptides were found for each of the bovine lymphocyte antigens (BoLA)-A11, -A20, -HD1, and -HD6 whereas no peptide was found for BoLA-HD7. Majority of the candidate peptides were from the viral glycoproteins. The contribution of such studies towards the identification of CTL epitopes of BHV-1 and other intracellular pathogens is discussed.

Primary characterization of a herpesvirus agent associated with Kaposi's sarcomae

Detection of novel DNA sequences in Kaposi's sarcoma (KS) and AIDS-related body cavity-based, non-Hodgkin's lymphomas suggests that these neoplasms are caused by a previously unidentified human herpesvirus. We have characterized this agent using a continuously infected B-lymphocyte cell line derived from an AIDS-related lymphoma and a genomic library made from a KS lesion. In this cell line, the agent has a large episomal genome with an electrophoretic mobility similar to that of 270-kb linear DNA markers during clamped homogeneous electric field gel electrophoresis. A 20.7-kb region of the genome has been completely sequenced, and within this region, 17 partial and complete open reading frames are present; all except one have sequence and positional homology to known gammaherpesvirus genes, including the major capsid protein and thymidine kinase genes. Phylogenetic analyses using both single genes and combined gene sets demonstrated that the agent is a gamma-2 herpesvirus (genus Rhadinovirus) and is the first member of this genus known to infect humans. Evidence for transient viral transmission from infected to uninfected cells is presented, but replication-competent virions have not been identified in infected cell lines. Sera from patients with KS have specific antibodies directed against antigens of infected cell lines, and these antibodies are generally absent in sera from patients with AIDS without KS. These studies define the agent as a new human herpesvirus provisionally assigned the descriptive name KS-associated herpesvirus; its formal designation is likely to be human herpesvirus 8.