Change in host cell tropism associated with in vitro replication of equine infectious anemia virus

Characterization of Equine Infectious Anemia Virus Long Terminal Repeat Quasispecies In Vitro and In Vivo

The equine infectious anemia virus (EIAV) attenuated vaccine was developed by long-term passaging of a field-isolated virulent strain in cross-species hosts, followed by successive cultivation in cells in vitro. To explore the molecular mechanism underlying the evolution of the EIAV attenuated vaccine, a systematic study focusing on long-terminal-repeat (LTR) variation in numerous virus strains ranging from virulent EIAV to attenuated EIAV was performed over time both in vitro and in vivo. Two hypervariable regions were identified within the U3 region in the enhancer region (EHR) and the negative regulatory element (NRE) and within the R region in the transcription start site (TSS) and the Tat-activating region (TAR). Among these sites, variation in the U3 region resulted in the formation of additional transcription factor binding sites; this variation of the in vitro-adapted strains was consistent with the loss of pathogenicity. Notably, the same LTR variation pattern was observed both in vitro and in vivo. Generally, the LTR variation in both the attenuated virus and the virulent strain fluctuated over time in vivo. Interestingly, the attenuated-virus-specific LTR variation was also detected in horses infected with the virulent strain, supporting the hypothesis that the evolution of an attenuated virus might have involved branching from EIAV quasispecies. This hypothesis was verified by phylogenetic analysis. The present systematic study examining the molecular evolution of attenuated EIAV from EIAV quasispecies may provide an informative model reflecting the evolution of similar lentiviruses.

IMPORTANCE The attenuated EIAV vaccine was the first lentiviral vaccine used to successfully control for equine infectious anemia in China. This vaccine provides an important reference for studying the relationship between EIAV gene variation and changes in biological characteristics. Importantly, the vaccine provides a model for the investigation of lentiviral quasispecies evolution. This study followed the “natural” development of the attenuated EIAV vaccine by use of a systematic analysis of LTR evolution in vitro and in vivo. The results revealed that the increase in LTR variation with passaging was accompanied by a decrease in virulence, which indicated that LTR variability might parallel the attenuation of virulence. Interestingly, the attenuated-virus-specific LTR variation was also detected in virulent-strain-infected horses, a finding consistent with those of previous investigations of gp90 and S2 evolution. Therefore, we present a hypothesis that the evolution of the attenuated virus may involve branching from EIAV quasispecies present in vivo.

The integration of a macrophage-adapted live vaccine strain of equine infectious anaemia virus (EIAV) in the horse genome

Integration is an important feature of retroviruses and retrovirus-based therapeutic transfection vectors. The non-primate lentivirus equine infectious anaemia virus (EIAV) primarily targets macrophages/monocytes in vivo. Investigation of the integration features of EIAV_DLV121 strains, which are adapted to donkey monocyte-derived macrophages (MDMs), is of great interest. In this study, we analysed the integration features of EIAV_DLV121 in equine MDMs during in vitro infection. Our previously published integration sites (IS) for EIAV_FDDV13 in fetal equine dermal (FED) cells were also analysed in parallel as references. Sequencing of the host genomic regions flanking the viral IS showed that reference sequence (RefSeq) genes were preferentially targeted for integration by EIAV_DLV121. Introns, AT-rich regions, long interspersed nuclear elements (LINEs) and DNA transposons were also predominantly biased toward viral insertion, which is consistent with EIAV_FDDV13 integration into the horse genome in FED cells. In addition, the most significantly enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, specifically gag junctions for EIAV_DLV121 and tight junctions for EIAV_FDDV13, are regulators of metabolic function, which is consistent with the common bioprocesses, specifically cell cycle and chromosome/DNA organization, identified by gene ontology (GO) analysis. Our results demonstrate that EIAV integration occurs in regions that harbour structural and topological features of local chromatin in both macrophages and fibroblasts. Our data on EIAV will facilitate further understanding of lentivirus infection and the development of safer and more effective gene therapy vectors.

[Mouse embryonic stem cells - a new cellular system for studying the equine infectious anemia virus in vitro and in vivo]

The complexity of the pathogenesis and insufficient knowledge about the slow retroviral infections, which include equine infectious anemia, necessitates finding an adequate laboratory model for the study of the infection process and immunogenesis to create means of prevention and treatment of diseases. Data about strains and cellular tropism of the virus are discussed. It was shown that mouse embryonic stem cells (ESCS) exhibited unique properties and characteristics. In contrast to fibroblasts and other cell types, these cells can be considered as a new cell system for studying EIAV in vitro and in vivo. Under differentiation-inducing conditions they are able to reproduce in vitro embryogenesis cells and form cells of three germ layers. Differentiation of mouse ESCs in the direction of hematopoiesis could contribute new knowledge and understanding of viral tropism EIAV in vitro. ESC can be returned back to the early pre-implantation embryo. Once in the germ cell environment, they participate in the formation of tissues and organs of the developing fetus. Thus, the adaptation of the mouse ESC to the equine EIAV through genetic transformation makes it possible to get closer to the creation of a laboratory model for the study of the in vivo immune response in the lentiviral infection.

Inhibition of lentivirus replication by aqueous extracts of Prunella vulgaris

Background

Various members of the mint family have been used historically in Chinese and Native American medicine. Many of these same family members, including Prunella vulgaris, have been reported to have anti-viral activities. To further characterize the anti-lentiviral activities of P. vulgaris, water and ethanol extractions were tested for their ability to inhibit equine infectious anemia virus (EIAV) replication.

Results

Aqueous extracts contained more anti-viral activity than did ethanol extracts, displaying potent anti-lentiviral activity against virus in cell lines as well as in primary cell cultures with little to no cellular cytotoxicity. Time-of-addition studies demonstrated that the extracts were effective when added during the first four h of the viral life cycle, suggesting that the botanical constituents were targeting the virion itself or early entry events. Further analysis revealed that the extracts did not destroy EIAV virion integrity, but prevented viral particles from binding to the surface of permissive cells. Modest levels of anti-EIAV activity were also detected when the cells were treated with the extracts prior to infection, indicating that anti-EIAV botanical constituents could interact with both viral particles and permissive cells to interfere with infectivity. Size fractionation of the extract demonstrated that eight of the nine fractions generated from aqueous extracts displayed anti-viral activity. Separation of ethanol soluble and insoluble compounds in the eight active fractions revealed that ethanol-soluble constituents were responsible for the anti-viral activity in one fraction whereas ethanol-insoluble constituents were important for the anti-viral activity in two of the other fractions. In three of the five fractions that lost activity upon sub-fractionation, anti-viral activity was restored upon reconstitution of the fractions, indicating that synergistic anti-viral activity is present in several of the fractions.

Conclusion

Our findings indicate that multiple Prunella constituents have profound anti-viral activity against EIAV, providing additional evidence of the broad anti-viral abilities of these extracts. The ability of the aqueous extracts to prevent entry of viral particles into permissive cells suggests that these extracts may function as promising microbicides against lentiviruses.

An equine infectious anemia virus variant superinfects cells through novel receptor interactions

Wild-type strains of equine infectious anemia virus (EIAV) prevent superinfection of previously infected cells. A variant strain of virus that spontaneously arose during passage, EIAV(vMA-1c), can circumvent this mechanism in some cells, such as equine dermis (ED) cells, but not in others, such as equine endothelial cells. EIAV(vMA-1c) superinfection of ED cells results in a buildup of unintegrated viral DNA and rapid killing of the cell monolayer. Here, we examined the mechanism of resistance that is used by EIAV to prevent superinfection and explored the means by which EIAV(vMA-1c) overcomes this restriction. We found that the cellular receptor used by EIAV, equine lentivirus receptor 1 (ELR1), remains on the surface of cells chronically infected with EIAV, suggesting that wild-type EIAV interferes with superinfection by masking ELR1. The addition of soluble wild-type SU protein to the medium during infection blocked infection by wild-type strains of virus, implicating SU as the viral protein responsible for interfering with virion entry into previously infected cells. Additionally, interference of wild-type EIAV binding to ELR1 by the addition of either anti-ELR1 antibodies or the ELR1 ectodomain prevented entry of the wild-type strains of EIAV into two permissive cell populations. Many of these same interference treatments prevented EIAV(vMA-1c) infection of endothelial cells but only modestly affected the ability of EIAV(vMA-1c) to enter and kill previously infected ED cells. These findings indicate that EIAV(vMA-1c) retains the ability to use ELR1 for entry and suggest that this virus can interact with an additional, unidentified receptor to superinfect ED cells.

Equine infectious anemia virus entry occurs through clathrin-mediated endocytosis

Entry of wild-type lentivirus equine infectious anemia virus (EIAV) into cells requires a low-pH step. This low-pH constraint implicates endocytosis in EIAV entry. To identify the endocytic pathway involved in EIAV entry, we examined the entry requirements for EIAV into two different cells: equine dermal (ED) cells and primary equine endothelial cells. We investigated the entry mechanism of several strains of EIAV and found that both macrophage-tropic and tissue culture-adapted strains utilize clathrin-coated pits for entry. In contrast, a superinfecting strain of EIAV, EIAV(vMA-1c), utilizes two mechanisms of entry. In cells such as ED cells that EIAV(vMA-1c) is able to superinfect, viral entry is pH independent and appears to be mediated by plasma membrane fusion, whereas in cells where no detectable superinfection occurs, EIAV(vMA-1c) entry that is low-pH dependent occurs through clathrin-coated pits in a manner similar to wild-type virus. Regardless of the mechanism of entry being utilized, the internalization kinetics of EIAV is rapid with 50% of cell-associated virions internalizing within 60 to 90 min. Cathepsin inhibitors did not prevent EIAV entry, suggesting that the low-pH step required by wild-type EIAV is not required to activate cellular cathepsins.

Long terminal repeat sequences from virulent and attenuated equine infectious anemia virus demonstrate distinct promoter activities

In the early 1970s, the Chinese Equine Infectious Anemia Virus (EIAV) vaccine, EIAV(DLA), was developed through successive passages of a wild-type virulent virus (EIAV(L)) in donkeys in vivo and then in donkey macrophages in vitro. EIAV attenuation and cell tropism adaptation are associated with changes in both envelope and long terminal repeat (LTR). However, specific LTR changes during Chinese EIAV attenuation have not been demonstrated. In this study, we compared LTR sequences from both virulent and attenuated EIAV strains and documented the diversities of LTR sequence from in vivo and in vitro infections. We found that EIAV LTRs of virulent strains were homologous, while EIAV vaccine have variable LTRs. Interestingly, experimental inoculation of EIAV(DLA) into a horse resulted in a restriction of the LTR variation. Furthermore, LTRs from EIAV(DLA) showed higher Tat transactivated activity than LTRs from virulent strains. By using chimeric clones of wild-type LTR and vaccine LTR, the main difference of activity was mapped to the changes of R region, rather than U3 region.

Immune selection of equine infectious anemia virus env variants during the long-term inapparent stage of disease

The principal neutralizing domain (PND) of equine infectious anemia virus (EIAV) is located in the V3 region of SU. Genetic variation in the PND is considered to play an important role in immune escape and EIAV persistence; however, few studies have characterized genetic variation in SU during the inapparent stage of disease. To better understand the mechanisms of virus persistence, we undertook a longitudinal study of SU variation in a pony experimentally inoculated with the virulent EIAV(Wyo). Viral RNA isolated from the inoculum and from sequential sera samples was amplified by RT-PCR, cloned, and individual clones were sequenced. Of the 147 SU clones obtained, we identified 71 distinct V3 variants that partitioned into five major non-overlapping groups, designated PND-1 to PND-5, which segregated with specific stages of clinical disease. Genotypes representative of each group were inserted into an infectious molecular clone, and chimeric viruses were tested for susceptibility to neutralization by autologous sera from successive times post-infection. Overall, there was a trend for increasing resistance to neutralizing antibody during disease progression. The PND genotype associated with recrudescence late in infection was resistant to both type-specific and broadly neutralizing antibody, and displayed a reduced replication phenotype in vitro. These findings indicate that neutralizing antibody exerts selective pressure throughout infection and suggest that viral strategies of immune evasion and persistence change in the face of an evolving and maturing host immune response.

Characterization of functional domains of equine infectious anemia virus Rev suggests a bipartite RNA-binding domain

Equine infectious anemia virus (EIAV) Rev is an essential regulatory protein that facilitates expression of viral mRNAs encoding structural proteins and genomic RNA and regulates alternative splicing of the bicistronic tat/rev mRNA. EIAV Rev is characterized by a high rate of genetic variation in vivo, and changes in Rev genotype and phenotype have been shown to coincide with changes in clinical disease. To better understand how genetic variation alters Rev phenotype, we undertook deletion and mutational analyses to map functional domains and to identify specific motifs that are essential for EIAV Rev activity. All functional domains are contained within the second exon of EIAV Rev. The overall organization of domains within Rev exon 2 includes a nuclear export signal, a large central region required for RNA binding, a nonessential region, and a C-terminal region required for both nuclear localization and RNA binding. Subcellular localization of green fluorescent protein-Rev mutants indicated that basic residues within the KRRRK motif in the C-terminal region of Rev are necessary for targeting of Rev to the nucleus. Two separate regions of Rev were necessary for RNA binding: a central region encompassing residues 57 to 130 and a C-terminal region spanning residues 144 to 165. Within these regions were two distinct, short arginine-rich motifs essential for RNA binding, including an RRDRW motif in the central region and the KRRRK motif near the C terminus. These findings suggest that EIAV Rev utilizes a bipartite RNA-binding domain.

Endocytosis and a low-pH step are required for productive entry of equine infectious anemia virus

Recently, it has become evident that entry of some retroviruses into host cells is dependent upon a vesicle-localized, low-pH step. The entry mechanism of equine infectious anemia virus (EIAV) has yet to be examined. Here, we demonstrate that wild-type strains of EIAV require a low-pH step for productive entry. Lysosomotropic agents that inhibit the acidification of internal vesicles inhibited productive entry of EIAV. The presence of ammonium chloride (30 mM), monensin (30 microM), or bafilomycin A (50 nM) in the medium dramatically decreased the number of EIAV antigen-positive cells. We found that a low-pH step was required for EIAV infection of tissue culture cell lines as well as primary cells, such as endothelial cells and monocyte-derived macrophages. The ammonium chloride treatment did not reduce virion stability, nor did the treatment prevent virion binding to cells. Consistent with a requirement for a low-pH step, virion infectivity was enhanced more than threefold by brief low-pH treatment following binding of viral particles to permissive cells. A superinfecting variant strain of EIAV, vMA-1c, did not require a low-pH step for productive infection of fibroblasts. However, lysosomotropic agents were inhibitory to vMA-1c infection in the other cell types that vMA-1c infected but did not superinfect, indicating that the entry pathway used by vMA-1c for superinfection abrogates the need for the low-pH step.

Evolution of the equine infectious anemia virus long terminal repeat during the alteration of cell tropism

Equine infectious anemia virus (EIAV) is a lentivirus with in vivo cell tropism primarily for tissue macrophages; however, in vitro the virus can be adapted to fibroblasts and other cell types. Tropism adaptation is associated with both envelope and long terminal repeat (LTR) changes, and findings strongly suggest that these regions of the genome influence cell tropism and virulence. Furthermore, high levels of genetic variation have been well documented in both of these genomic regions. However, specific EIAV nucleotide or amino acid changes that are responsible for cell tropism changes have not been identified. A study was undertaken with the highly virulent, macrophage-tropic strain of virus EIAV(wyo) to identify LTR changes associated with alterations in cell tropism. We found the stepwise generation of a new transcription factor binding motif within the enhancer that was associated with adaptation of EIAV to endothelial cells and fibroblasts. An LTR that contained the new motif had enhanced transcriptional activity in fibroblasts, whereas the new site did not alter LTR activity in a macrophage cell line. This finding supports a previous prediction that selection for new LTR genetic variants may be a consequence of cell-specific selective pressures. Additional investigations of the EIAV(wyo) LTR were performed in vivo to determine if LTR evolution could be detected over the course of a 3-year infection. Consistent with previous in vivo findings, we observed no changes in the enhancer region of the LTR over that time period, indicating that the EIAV(wyo) LTR was evolutionarily stable in vivo.

Subpopulations of equine infectious anemia virus Rev coexist in vivo and differ in phenotype

Lentiviruses exist in vivo as a population of related, nonidentical genotypes, commonly referred to as quasispecies. The quasispecies structure is characteristic of complex adaptive systems and contributes to the high rate of evolution in lentiviruses that confounds efforts to develop effective vaccines and antiviral therapies. Here, we describe analyses of genetic data from longitudinal studies of genetic variation in a lentivirus regulatory protein, Rev, over the course of disease in ponies experimentally infected with equine infectious anemia virus. As observed with other lentivirus data, the Rev variants exhibited a quasispecies character. Phylogenetic and partition analyses suggested that the Rev quasispecies comprised two distinct subpopulations that coexisted during infection. One subpopulation appeared to accumulate changes in a linear, time-dependent manner, while the other evolved radially from a common variant. Over time, the two subpopulations cycled in predominance coincident with changes in the disease state, suggesting that the two groups differed in selective advantage. Transient expression assays indicated the two populations differed significantly in Rev nuclear export activity. Chimeric proviral clones containing Rev genotypes representative of each population differed in rate and overall level of virus replication in vitro. The coexistence of genetically distinct viral subpopulations that differ in phenotype provides great adaptability to environmental changes within the infected host. A quasispecies model with multiple subpopulations may provide additional insight into the nature of lentivirus reservoirs and the evolution of antigenic and drug-resistant variants.

Characterization of a cytolytic strain of equine infectious anemia virus

A novel strain of equine infectious anemia virus (EIAV) called vMA-1c that rapidly and specifically killed infected equine fibroblasts (ED cells) but not other infectible cell lines was established. This strain was generated from an avirulent, noncytopathic strain of EIAV, MA-1. Studies with this new cytolytic strain of virus have permitted us to define viral parameters associated with EIAV-induced cell killing and begin to explore the mechanism. vMA-1c infection resulted in induction of rapid cell death, enhanced fusogenic activity, and increased rates of spread in equine fibroblasts compared to other strains of EIAV. The highly cytolytic nature of vMA-1c suggested that this strain might be superinfecting equine fibroblasts. Receptor interference studies demonstrated that prior infection of equine fibroblasts with EIAV did not alter the ability of vMA-1c to infect and kill these cells. In similar studies in a canine fibroblast cell line, receptor interference did occur. vMA-1c infection of equine fibroblasts was also associated with large quantities of unintegrated viral DNA, a well-established hallmark of retroviral superinfection. Cloning of the vMA-1c genome identified nucleotide changes that would result in at least one amino acid change in all viral proteins. A chimeric infectious molecular clone containing the vMA-1c tat, S2, and env open reading frames recapitulated most of the characteristics of vMA-1c, including superinfection, fibroblast killing, and fusogenic activity. In summary, in vitro selection for a strain of EIAV that rapidly killed cells resulted in the generation of a virus that was able to superinfect these cells, presumably by the use of a novel mechanism of cell entry. This phenotype mapped to the 3' half of the genome.

Epithelial cells from goat oviduct are highly permissive for productive infection with caprine arthritis-encephalitis virus (CAEV)

Caprine oviduct epithelial cells (COEC) are commonly used in in vitro goat embryo production protocols to stimulate early embryonic development. These feeder cells are usually collected from slaughterhouses from unknown serological status animals for caprine arthritis-encephalitis virus (CAEV) infection which is frequent in many regions of the world. Tissues derived from this source may be contaminated with CAEV and the use of such material in in vitro fertilisation systems may contribute to transmission of this pathogen to the cultured embryos and dissemination via embryo transfer (ET). The aim of this study was to determine the permissiveness of COEC to CAEV replication in vitro. Cells were isolated from goats from certified CAEV-free herds and then were inoculated with two CAEV strains: the molecularly-cloned isolate of CAEV (CAEV-pBSCA) and the French field isolate (CAEV-3112). Cytopathic effects (CPE) were observed on cell culture monolayers inoculated with both CAEV strains. Expression of CAEV proteins was shown both by immunocytochemistry using anti-p24 gag specific antibodies and by immunoprecipitation using a hyperimmune serum. The CAEV proteins were correctly and properly processed by artificially-infected COEC and the titers of virus released into the supernatant reached 10(6) TCID(50)/ml 6 days post-inoculation. Although the macrophage lineage cells are the main centre of infection in the virus-positive animal, these findings suggest that epithelial cells may be important in the viral life cycle probably as a reservoir allowing the viral persistence, dissemination and pathogenesis. These results suggest also that the use in in vitro fertilisation systems of co-culture feeder cells that support efficient replication of CAEV to high titers could represent a serious risk for permanent transmission of virus to the cultured embryos and to the surrogate dam involved.

Efficient replication of caprine arthritis-encephalitis virus in goat granulosa cells

Recent reports demonstrated the susceptibility of epithelial cells from different organs to caprine arthritis-encephalitis virus (CAEV) both in vitro and in vivo. Since granulosa cells (GC) are of epithelial origin and currently used for in vitro oocyte maturation, we addressed the question whether these cells are susceptible or resistant to CAEV infection. GC were isolated from goats from certified CAEV-free herds. PCR analysis on GC DNA using CAEV specific primers confirmed the absence of CAEV infection and immunocytochemistry using specific K813 anti-cytokeratin monoclonal antibodies confirmed the epithelial nature of GC. These cells were then inoculated with CAEV using two strains: the CAEV-pBSCA molecular clone and the CAEV-3112 French field isolate. Cytopathic effects (CPE) were observed on cell culture monolayers inoculated with both CAEV strains. Expression of CAEV proteins was shown both by immunocytochemistry using anti-p24 gag specific antibodies and by immunoprecipitation using an hyperimmune serum. Supernatant of infected cells were shown to contain high titers (ranging 10(5) tissue culture infectious doses 50 per ml: TCID(50) per ml) of infectious cytopathic viruses when assayed onto the indicator goat synovial membrane (GSM) cells. Our findings demonstrate the large cell tropism of CAEV and suggest that GC could serve as a reservoir for the virus during the sub-clinical phase of infection. Furthermore, given the high seroprevalence of CAEV in the all industrialised countries and the large number of ovaries derived from unknown serological status animals used for in vitro goat embryo production, one can conclude that these feeder cell cultures might be a potential source of early transmission of CAEV to goat embryos.

DH82 cells: a macrophage cell line for the replication and study of equine infectious anemia virus

In vivo, tissue macrophages have been implicated as an important cell for the replication of equine infectious anemia virus (EIAV). Laboratory investigations of EIAV/macrophage interactions, however, have been hampered by the laborious blood monocyte isolation procedures. In addition, adherent equine macrophage cultures generally have poor long-term viability and are resistant to transfection. This report describes an adherent canine macrophage-like cell line, DH82, that supports the replication of EIAV. This cell line was easily transfectable and supported EIAV Tat transactivation of the LTR. Electrophoretic mobility shift assays were carried out to determine which transcription factor binding sites within the LTR enhancer region were bound by DH82 nuclear extracts. It was found that five different motifs were occupied. The ets motifs that are bound by PU.1 in primary macrophage nuclear extracts specifically interacted with DH82 nuclear extracts. In addition, the PEA-2, Lvb and Oct motifs that are occupied by fibroblast nuclear extracts were also bound by DH82 nuclear extracts. Finally, the methylation-dependent binding protein (MDBP) site that is bound by all nuclear extracts investigated to date demonstrated specific interactions with DH82 nuclear extracts. The observation that both macrophage-specific and fibroblast-specific motifs were utilized by DH82 nuclear extracts suggested that both macrophage-adapted and fibroblast-adapted EIAV could replicate in DH82 cells. Indeed, infectivity studies demonstrated that strains of virus that exclusively replicate in macrophages can replicate in DH82 cells and fibroblast-adapted strains of virus can also replicate in these cells. Finally, these cells could be transfected readily with the EIAV molecular clone, pSPeiav19-2, and virus spread was detected within the culture. In conclusion, this study has identified a useful cell line that should facilitate the study of EIAV expression and replication.

Freqüência de anemia infecciosa em eqüinos no Acre, 1986 a 1996

Foram analisadas as fichas de 9.963 eqüídeos do Acre, submetidos ao teste de imunodifusão em gel de ágar (IDGA) para anemia infecciosa eqüina (AIE), no período de 1986 a 1996. As regiões sócio-ecológicas da Bacia do Alto Juruá, Alto Acre e Alta Bacia do Purus apresentaram os maiores índices da doença, o que caracteriza a associação entre região e positividade. Essas áreas são fronteiriças com o Peru, Bolívia e o Estado do Amazonas, são distantes de Rio Branco, capital do Estado, onde muitas vezes é difícil o acesso pelas estradas, revelando serem áreas de risco. As regiões Oriental e Rio Branco apresentaram baixos índices de positividade. Não se observou diferença estatística entre animais positivos e negativos quanto à espécie, sexo, raça e idade.

Detection of horses infected naturally with equine infectious anemia virus by nested polymerase chain reaction

A nested polymerase chain reaction (PCR) amplifying a region of the gag gene of equine infectious anemia virus (EIAV) was developed for the rapid and direct detection of proviral DNA from the peripheral blood of naturally infected horses and was compared with the Coggins test. DNA prepared from white blood cells of 122 field horses from 15 stables with reported cases of EIAV and one seronegative stable were analysed. Amplifications of expected size fragments were obtained by nested PCR for 88 horses using two different sets of primers targeting the gag region. The specificity of the amplified products was confirmed by hybridization using a digoxigenin-labeled probe. Gag-nested PCR-restriction fragment length polymorphism analysis distinguished two different subtypes of gag gene, A and B. Subtype A was found to be the most prevalent among the infected horses that were tested. The PCR-gag amplified sequence of subtype A shared 84.6% nucleotide and 93% deduced amino acid sequence identities with the prototype Wyoming strain whereas subtype B sequence was almost 100% identical to the prototype. Sequence analysis of gag subtype A suggests the presence of a novel EIAV variant among infected horses in Canada. The nested PCR assay developed in the present study detected more EIAV positive animals and was found as specific as the agar gel immunodiffusion (Coggins) assay and offers great potential a diagnostic test for the detection of EIAV infections in field horses.

Regulation of equine infectious anemia virus expression

Equine infectious anemia virus (EIAV) is an ungulate lentivirus that is related to human immunodeficiency virus (HIV). Much of the understanding of lentiviral gene regulation comes from studies using HIV. HIV studies have provided insights into molecular regulation of EIAV expression; however, much of the regulation of EIAV expression stands in stark contrast to that of HIV. This review provides an overview of the current state of knowledge of EIAV regulation by comparing and contrasting EIAV gene regulation to HIV. The role of EIAV gene regulation is discussed in relation to EIAV pathogenesis.

Aminoglycoside-arginine conjugates that bind TAR RNA: synthesis, characterization, and antiviral activity

Regulation of HIV gene expression is crucially dependent on binding of the trans-activator protein, Tat, to the trans-activation response RNA element, TAR, found at the 5' end of all HIV-1 transcripts. Tat-TAR interaction is mediated by a short arginine-rich domain of the protein. Disruption of this interaction could, in theory, create a state of complete viral latency. A new class of small-molecule peptidomimetic TAR RNA binders, conjugates of aminoglycosides and arginine, was recently designed [Litovchick, A., Evdokimov, A. G., and Lapidot, A. (1999) FEBS Lett. 445, 73-79]. Two of these compounds, the tri-arginine derivative of gentamicin C (R3G) and the tetra-arginine derivative of kanamycin A (R4K), bind efficiently and specifically to TAR RNA. These compounds display negligible toxicity while being transported and accumulated in cell nuclei. Here we present a detailed synthesis and chemical characterization of the aminoglycoside-arginine conjugates R3G and R4K as well as GB4K, the tetra-gamma-guanidinobutyric derivative of kanamycin A. Their binding sites on TAR RNA were assigned by RNase A, uranyl nitrate, and lead acetate footprinting. The conjugates interact with TAR RNA in the widened major groove, formed by the UCU bulge and the neighboring base pairs of the upper stem portion of TAR, the binding site of Tat protein, and Tat-derived peptides (e.g., R52). Our results suggest an additional binding site of R4K and R3G compounds, in the lower stem-bulge region of TAR. The antiviral activity of the conjugates in cultured equine dermal fibroblasts infected with equine infectious anemia virus, used as a model system of HIV-infected cells, is also presented.

Cell specificity of the transcription-factor repertoire used by a lentivirus: motifs important for expression of equine infectious anemia virus in nonmonocytic cells

The equine infectious anemia virus (EIAV) long-terminal repeat (LTR) has been identified as highly variable, both in infected horses and in cell culture. This nucleotide hypervariation is localized to the LTR enhancer region. The EIAV LTR has been implicated in controlling both the cell tropism and virulence of the virus and it is postulated that the enhancer-region hypervariation may be responsible for the LTR effects. Our previous studies have demonstrated that the presence of DNA motifs bound by the ets transcription-factor family member PU.1 are critically important for EIAV expression in equine macrophages. Here we identify and characterize the EIAV LTR enhancer motifs PEA-2, Lvb, Oct, and CRE, that bind to fibroblast nuclear extracts. Three of these four motifs, PEA-2, Oct, and CRE, were determined to be important for expression of the LTR in a fibroblast cell line that supports productive infection of EIAV. These motifs that are important for expression of the LTR in fibroblasts were found to be interdigitated between the PU.1 sites. We hypothesize that the combination of motif interdigitation and cell-specific usage of these motifs may be responsible for the observed EIAV LTR enhancer-region hypervariation.

Replication ability in vitro and in vivo of equine infectious anemia virus avirulent Japanese strain

An attenuated equine infectious anemia virus (EIAV), V26, was previously prepared by 50 passages of the Japanese virulent strain V70 in primary horse macrophage culture. The horses inoculated with this V26 virus were shown to raise neutralizing antibodies against V70 without any viremia. Here, we investigated the in vitro and in vivo replication ability of V26. Comparison of the long-terminal repeat (LTR) sequences between V26 and V70 revealed a large insertion within the LTR U3 hypervariable region of V26. V26 with the mutation in the LTR showed much higher promoter activity in vitro than V70. This is consistent with the much higher replication rate of V26 in horse primary macrophage cultures compared with V70. In sharp contrast, we failed to identify the V26-specific LTR sequence by PCR, at least in sequential samples of plasma or peripheral blood mononuclear cells derived from three horses until day 62 after V26 inoculation. In contrast, antibody responses to EIAV were observed in all horses. The results suggest that the replication ability of V26 in vivo is extremely low. When one of the horses was subsequently challenged with cell-associated V70, it was found that the horse became PCR positive for EIAV. There was no LTR mutation in EIAV genome in samples periodically prepared from the V70-challenged horse. Thus it was suggested that the LTR mutation in EIAV, which occurs during serial passage in vitro, affects EIAV replication in vitro and in vivo.

Endothelial cell infection in vivo by equine infectious anaemia virus

Equine infectious anaemia virus (EIAV) infection of horses is characterized clinically by recurrent episodes of fever, thrombocytopenia and anaemia. In vivo, the only site of virus replication that has been previously demonstrated for EIAV is the tissue macrophage. In this study, in situ hybridization for EIAV was combined with immunohistochemistry for cell-type-specific markers to identify infected endothelial cells. EIAV-infected endothelial cells and macrophages were detected in horses infected with either virulent wild-type or with weakly virulent tissue culture-adapted strains of EIAV. The role of endothelial cell infection in the pathogenesis of EIAV remains undefined, but could contribute to the development of thrombocytopenia. However, endothelial cell infection does not appear to be a determinant of virulence for EIAV.

Photoactivated virucidal properties of tridentate 2,2'-dihydroxyazobenzene and 2-salicylideneaminophenol platinum pyridine complexes

The potent photoactivated virucidal activity of tridentate 2,2'-dihydroxyazobenzene- and 2-salicylideneaminophenol platinum pyridine complexes 1, 2, 4, 6, 7, 9, and 10 against enveloped viruses (e.g., EIAV, HIV, and HSV) is described.

Equine endothelial cells support productive infection of equine infectious anemia virus

Previous cell infectivity studies have demonstrated that the lentivirus equine infectious anemia virus (EIAV) infects tissue macrophages in vivo and in vitro. In addition, some strains of EIAV replicate to high titer in vitro in equine fibroblasts and fibroblast cell lines. Here we report a new cell type, macrovascular endothelial cells, that is infectible with EIAV. We tested the ability of EIAV to infect purified endothelial cells isolated from equine umbilical cords and renal arteries. Infectivity was detected by cell supernatant reverse transcriptase positivity, EIAV antigen positivity within individual cells, and the detection of viral RNA by in situ hybridization. Virus could rapidly spread through the endothelial cultures, and the supernatants of infected cultures contained high titers of infectious virus. There was no demonstrable cell killing in infected cultures. Three of four strains of EIAV that were tested replicated in these cultures, including MA-1, a fibroblast-tropic strain, Th.1, a macrophage-tropic strain, and WSU5, a strain that is fibroblast tropic and can cause disease. Finally, upon necropsy of a WSU5-infected horse 4 years postinfection, EIAV-positive endothelial cells were detected in outgrowths of renal artery cultures. These findings identify a new cell type that is infectible with EIAV. The role of endothelial cell infection in the course of equine infectious anemia is currently unknown, but endothelial cell infection may be involved in the edema that can be associated with infection. Furthermore, the ability of EIAV to persistently infect endothelial cultures and the presence of virus in endothelial cells from a long-term carrier suggest that this cell type can serve as a reservoir for the virus during subclinical phases of infection.

Biological characterization of Rev variation in equine infectious anemia virus

Sequence analysis identified significant variation in the second exon of equine infectious anemia virus (EIAV) rev. Functional analysis indicated that limited amino acid variation in Rev significantly altered the export activity of the protein but did not affect Rev-dependent alternative splicing. EIAV Rev can mediate export through two independent cis-acting Rev-responsive elements (RREs), and differences among Rev variants were more pronounced when both RREs were present. Variation in Rev may be an important mechanism for regulation of virus replication in vivo and may contribute to changes in clinical disease.

Development and characterization of an in vivo pathogenic molecular clone of equine infectious anemia virus

An infectious nonpathogenic molecular clone (19-2-6A) of equine infectious anemia virus (EIAV) was modified by substitution of a 3.3-kbp fragment amplified by PCR techniques from a pathogenic variant (EIAV(PV)) of the cell culture-adapted strain of EIAV (EIAV(PR)). This substitution consisted of coding sequences for 77 amino acids at the carboxyl terminus of the integrase, the S1 (encoding the second exon of tat), S2, and S3 (encoding the second exon of rev) open reading frames, the complete env gene (including the first exon of rev), and the 3' long terminal repeat (LTR). Modified 19-2-6A molecular clones were designated EIAV(PV3.3), and infection of a single pony (678) with viruses derived from a mixture of five of these molecular clones induced clinical signs of acute equine infectious anemia (EIA) at 23 days postinfection (dpi). As a consequence of this initial study, a single molecular clone, EIAV(PV3.3#3) (redesignated EIAV(UK)), was selected for further study and inoculated into two ponies (613 and 614) and two horses (700 and 764). Pony 614 and the two horses developed febrile responses by 12 dpi, which was accompanied by a 48 to 64% reduction in platelet number, whereas pony 613 did not develop fever (40.6 degrees C) until 76 dpi. EIAV could be isolated from the plasma of these animals by 5 to 7 dpi, and all became seropositive for antibodies to this virus by 21 dpi. Analysis of the complete nucleotide sequence demonstrated that the 3.3-kbp 3' fragment of EIAV(UK) differed from the consensus sequence of EIAV(PV) by just a single amino acid residue in the second exon of the rev gene. Complete homology with the EIAV(PV) consensus sequence was observed in the hypervariable region of the LTR. However, EIAV(UK) was found to contain an unusual 68-bp nucleotide insertion/duplication in a normally conserved region of the LTR sequence. These results demonstrate that substitution of a 3.3-kbp fragment from the EIAV(PV) strain into the infectious nonpathogenic molecular clone 19-2-6A leads to the production of progeny virus particles with the ability to induce clinical signs of EIA. Therefore, EIAV(UK), which is the first pathogenic, cell culture-adapted molecular clone of EIAV to be described, should be of value in identifying viral determinants of pathogenicity.

Disease induction by virus derived from molecular clones of equine infectious anemia virus

Equine infectious anemia virus (EIAV), a macrophage-tropic lentivirus, causes persistent infections of horses. A number of biologic features, including the rapid development of acute disease, the episodic nature of chronic disease, the propensity for viral genetic variation, and the ability for many infected animals to eventually control virus replication, render EIAV a potentially useful model system for the testing of antiretroviral therapies and vaccine strategies. The utility of the EIAV system has been hampered by the lack of proviral clones that encode promptly pathogenic viral stocks. In this report, we describe the generation and characterization of two infectious molecular clones capable of causing acute clinical syndromes similar to those seen in natural infections. Virus derived from clone p19/wenv17 caused severe debilitating disease at 5 to 7 days postinfection; initial febrile episodes were fatal in two of three infected animals. Virus derived from a second clone, p19/wenv16, caused somewhat milder primary febrile episodes by 10 to 12 days postinfection in two of two infected animals. Virus derived from both clones caused persistent infections such that some animals exhibited chronic equine infectious anemia, characterized by multiple disease episodes. The two virulent clones differ in envelope and rev sequences.

Localized sequence heterogeneity in the long terminal repeats of in vivo isolates of equine infectious anemia virus

The role of in vivo long terminal repeat (LTR) sequence variation of the lentivirus equine infectious anemia virus (EIAV) has not been explored. In this study, we investigated the heterogeneity found in the LTR sequences from seven EIAV-seropositive horses: three horses with clinical disease and four horses without any detectable signs of disease. LTR sequences were targeted in this study because the LTR U3 enhancer region of tissue culture-derived isolates has been identified as one of the few hypervariable regions of the EIAV genome. Furthermore, LTR variation may regulate EIAV expression in vivo. Both intra- and interanimal sequence variations were investigated. The intra-animal variation was low in seropositive, healthy horses (on average 0.44%). Intra-animal variation was consistently higher in clinically ill horses (0.99%), suggesting that greater numbers of quasispecies of EIAV are present when active virus replication is ongoing. Interanimal comparisons of consensus sequences generated from each horse demonstrated that the enhancer region is a hotspot of sequence variation in vivo. Thirty-seven of the 83 nucleotides that compose the U3 enhancer region were variable between the different in vivo-derived LTRs. The remainder of the LTR that was analyzed was more conserved, 8 of 195 nucleotide positions being variable. Results of electrophoretic mobility shift assays demonstrated that some nucleotide substitutions that occurred in the enhancer region eliminated or altered transcription factor binding motifs that are known to be important for EIAV LTR expression. These data suggested that the selective pressures exerted on the EIAV LTR enhancer sequences are different from those exerted on the remainder of the LTR. Our findings are consistent with the possibility that enhancer sequence hypervariability can alter expression of the virus in tissue macrophages and therefore contribute to clinical disease in infected horses.

Tumor necrosis factor-alpha production and disease severity after immunization with enriched major core protein (p26) and/or infection with equine infectious anemia virus

Cardinal features of equine infectious anemia (EIA) include fever, hemolytic anemia and thrombocytopenia during the acute phase of the disease, and cachexia and anemia seen during the chronic phase. These signs are thought to result from the release of inflammatory cytokines such as TNF-alpha. In order to determine if TNF-alpha has a role in the pathogenesis of acute EIA and vaccine-induced disease enhancement, we measured plasma concentrations of TNF-alpha in ponies immunized with virus enriched major core protein-p26 and/or experimentally infected with EIAV. Naturally infected inapparent EIAV carriers were also studied. TNF-alpha levels were determined by means of a WEHI 164, clone 13 cytotoxicity assay. We show a significant positive temporal correlation between TNF-alpha levels, severity of symptoms (fever and thrombocytopenia) and viremia. Furthermore, TNF-alpha levels also correlate with strain virulence and the disease enhancement seen in vaccinated ponies. Of this group of animals, those challenged with a heterologous virulent strain presented the most unfavorable outcome as well as the highest levels of TNF-alpha and viremia. The TNF-alpha activity observed in the bioassay was completely abrogated by a polyclonal rabbit anti-human TNF-alpha antiserum, thus confirming the specificity of the plasma cytotoxicity. Our observations indicate that TNF-alpha production correlates with the outcome of infection with EIAV.

Serologic evidence for bovine immunodeficiency virus infection in France

We report herein on the first serologic detection of antibodies to bovine immunodeficiency virus (BIV) in France. Serum samples from dairy and beef cattle from southwestern and western France (Landes and Vendée) were tested using a western blot assay with a recombinant 53 kDa gag precursor derived from the Louisiana BIV R29 isolate. We performed our study on the oldest animals from 37 different herds that were under serologic follow up for previous bovine leukemia virus infection. Overall, 398 selected bovine sera were assayed and 15 serum samples from 8 herds reacted with the recombinant 53 kDa BIV R29 gag. Interestingly, reactions obtained with French sera were weaker than with positive Louisiana sera, a finding that may indicate the occurrence of distinct French and Louisiana BIV variants.

Monocyte maturation controls expression of equine infectious anemia virus

In vivo, equine infectious anemia virus (EIAV) replicates in tissues rich in macrophages, and it is widely believed that the tissue macrophage is the principal, if not sole, cell within the host that replicates virus. No viral replication has been detected in circulating peripheral blood monocytes. However, proviral DNA can be detected in these cells, and monocytes may serve as a reservoir for the virus. In this study, an in vitro model was developed to clarify the role of monocyte maturation in regulating EIAV expression. Freshly isolated, nonadherent equine peripheral blood monocytes were infected with a macrophage-tropic strain of EIAV, and expression of EIAV was monitored in cells held as nonadherent monocytes and cells allowed to adhere and differentiate into macrophages. A 2- to 3-day delay in viral antigen expression was observed in the nonadherent cells. This restriction of viral expression in monocytes was supported by nuclear run-on studies demonstrating that on day 5 postinfection, the level of actively transcribed viral messages was 4.7-fold lower in monocyte cultures than in macrophage cultures. Electrophoretic mobility shift assays identified three regions of the U3 enhancer that interacted with nuclear extracts from normal equine macrophages. Each region contained the core binding motif of a family of transcription factors that includes the product of the proto-oncogene ets. Antibodies to the Ets family member PU.1 caused a supershifting of retarded bands in an electrophoretic mobility shift assay. Transfection studies of ets motif mutants demonstrated that the U3 ets sites were important in the regulation of EIAV transcription in macrophages. Interactions between the ets motif and nuclear extracts from freshly isolated, nonadherent monocytes, macrophages adherent for 1 or 2 days, or macrophages adherent for 5 days gave different patterns of retarded bands, although the binding specificities were similar with all three extracts. The different complexes formed by monocyte and macrophage nuclear extracts may explain the enhanced ability of mature macrophages to support EIAV expression.

In vivo replicative status and envelope heterogeneity of equine infectious anemia virus in an inapparent carrier

The distribution and replicative status of equine infectious anemia virus (EIAV) DNA in the tissues of a well-characterized inapparent carrier horse were established by using the PCR technique. The EIAV pol region could be amplified in all of the tissues tested, including the cerebellum and periventricular tissue, at concentrations approximately 10(5)-fold less than in the same tissue from an acutely infected horse. Further analysis of the EIAV genome, with primer pairs diagnostic for sequential stages of reverse transcription, suggests that EIAV DNA in the brain, liver, and lymph nodes was incompletely synthesized. The products of reverse transcription were found to diminish progressively during first-strand synthesis, while products indicative of second-strand synthesis were observed only in kidney and spleen DNA samples. Sequences specific for different regions of the envelope could not be amplified from any of the tissues of the inapparent carrier, suggesting that the envelope is highly variable and may be subject to extensive drift. Together, the data suggest that low levels of EIAV replication persist without causing clinical disease in an inapparent carrier.

Isolation and characterization of new wild-type isolates of bovine lentivirus

Two new isolates of bovine lentivirus, also known as bovine immunodeficiency-like virus (BIV), were obtained from a seropositive cattle herd in Florida. This is the first report of new isolates of BIV since the original BIV strain, R29, was isolated in 1969. The two new BIV isolates were derived from blood buffy coat cells cocultivated in vitro with fetal bovine lung cell cultures. The new isolates differed in vitro from the original R29 isolate in replication and syncytium formation in fetal bovine lung cells. Both new isolates were confirmed as BIV by immunofluorescence assay, Western blotting (immunoblotting), and polymerase chain reaction. Sequence analyses of the polymerase chain reaction pol gene product showed 92.6 and 93.6% homology to the published nucleotide sequence of BIV R29-127, a molecular clone derived from BIV R29. Each of the new BIV isolates was inoculated into two calves, and virus was recovered between 5 and 10 days postinoculation (p.i.), with BIV seroconversion between 10 and 21 days p.i. Virus was recoverable and antibody was detectable for at least 4 months p.i. Two calves developed a transiently elevated mononuclear cell count, similar to what was reported for BIV R29 in the original experimental calf inoculations. No other clinical abnormalities were observed.

Identification of transactivation-response sequences in the long terminal repeat of bovine immunodeficiency-like virus

Transient expression assays using the reporter gene that encodes chloramphenicol acetyltransferase were used to identify cis-acting sequences necessary for bovine immunodeficiency-like virus (BIV) transactivation. Computer analyses identified two RNA stem-loop structures located immediately downstream of the transcription start site in the long terminal repeat. Deletion analysis of the long terminal repeat indicated that sequences containing the proximal stem-loop structure located between +4 and +31 are required for virus-specific transactivation. Therefore, BIV likely utilizes a mechanism of transactivation similar to that of the human and simian lentiviruses.

Analysis of multiple mRNAs from pathogenic equine infectious anemia virus (EIAV) in an acutely infected horse reveals a novel protein, Ttm, derived from the carboxy terminus of the EIAV transmembrane protein

Transcription of pathogenic equine infectious anemia virus (EIAV) in an acutely infected horse was examined by using the polymerase chain reaction and nucleotide sequencing. Four spliced transcripts were identified in liver tissue, in contrast to the multiplicity of alternatively spliced messages reported for in vitro-propagated human immunodeficiency virus, simian immunodeficiency virus, and, to a lesser extent, EIAV. Nucleotide sequence analysis demonstrated that three of these mRNAs encode known viral proteins: the envelope precursor, the product of the S2 open reading frame, and the regulatory proteins Tat and Rev. The fourth transcript encodes a novel Tat-TM fusion protein, Ttm. Ttm is a 27-kDa protein translated from the putative tat CTG initiation codon and containing the carboxy-terminal portion of TM immediately downstream from the membrane-spanning domain. p27ttm is expressed in EIAV-infected canine cells and was recognized by peptide antisera against both Tat and TM. Cells transfected with ttm cDNA also expressed p27ttm, which appeared to be localized to the endoplasmic reticulum or Golgi apparatus by indirect immunofluorescence. The carboxy terminus of lentiviral TM proteins has previously been shown to influence viral infectivity, growth kinetics, and cytopathology, suggesting that Ttm plays an important role in the EIAV life cycle.

Wild-type equine infectious anemia virus replicates in vivo predominantly in tissue macrophages, not in peripheral blood monocytes

In situ hybridization of tissues from two horses infected with the wild-type Wyoming strain of equine infectious anemia virus (EIAV) identified the liver, spleen, lymph nodes, kidney, lung, and adrenal gland as the primary host tissue sites for viral transcription during acute infection. Combined immunohistochemistry, with a monoclonal antibody recognizing a cytoplasmic antigen of equine mononuclear phagocytes, and in situ hybridization for viral RNA identified most infected cells as mature tissue macrophages. In contrast, in situ hybridization of adherent peripheral blood mononuclear cells collected from horses on various days during the first 2 weeks postinfection with the Wyoming strain of EIAV failed to detect any viral RNA in these cells. For the two horses described here, serum reverse transcriptase activity correlated directly with the degree of replication detected in tissue macrophages on the day of sacrifice. These results suggest that unlike other lentivirus infections in which mature tissue macrophages accumulate cytoplasmic viral RNA to a high level but fail to produce infectious virions, mature tissue macrophages are the likely primary source of the high titer of viremia present during acute infection with EIAV. No significant posttranscriptional block of viral replication in tissue macrophages appears to occur with EIAV.

The surface envelope protein gene region of equine infectious anemia virus is not an important determinant of tropism in vitro

Virulent, wild-type equine infectious anemia virus (EIAV) is restricted in one or more early steps in replication in equine skin fibroblast cells compared with cell culture-adapted virus, which is fully competent for replication in this cell type. We compared the sequences of wild-type EIAV and a full-length infectious proviral clone of the cell culture-adapted EIAV and found that the genomes were relatively well conserved with the exception of the envelope gene region, which showed extensive sequence differences. We therefore constructed several wild-type and cell culture-adapted virus chimeras to examine the role of the envelope gene in replication in different cell types in vitro. Unlike wild-type virus, which is restricted by an early event(s) for replication in equine dermis cells, the wild-type outer envelope gene chimeras are replication competent in this cell type. We conclude that even though there are extensive sequence differences between wild-type and cell culture-adapted viruses in the surface envelope gene region, this domain is not a determinant of the differing in vitro cell tropisms.

Characterization of early pathogenic effects after experimental infection of calves with bovine immunodeficiency-like virus

The early pathogenic effects of bovine immunodeficiency-like virus (BIV) were studied in calves experimentally inoculated with BIV. All animals inoculated with BIV R29-infected cells seroconverted by 6 weeks postinoculation, and BIV was recoverable from each animal at 2 weeks postinoculation. However, levels of BIV replication in vivo appeared to be low. In situ hybridization studies indicated that during peak periods of viral replication in vivo, less than 0.03% of peripheral blood mononuclear cells were expressing detectable levels of viral RNA. Moreover, the levels of viral RNA in these cells in vivo were less than 1/10 the levels observed in persistently infected cells in vitro. BIV-inoculated calves had significantly higher numbers of circulating lymphocytes, and follicular hyperplasia was observed in lymph nodes, hemal nodes, and spleen. The histopathological changes observed in BIV-infected calves were similar to changes found early after infection with the immunosuppressive lentiviruses, including human immunodeficiency virus type 1.

Preservation of natural endothelial cytopathogenicity of cytomegalovirus by propagation in endothelial cells

Cytomegalovirus (CMV) is a source of major complications in immunosuppressed individuals, and endothelial involvement in CMV infection is well documented. Traditionally the virus has been propagated in fibroblasts, however this process may alter CMV's characteristics, thereby limiting the fibroblast model's utility as a research tool. In our efforts to develop a more accurate in vitro model of CMV/endothelial cell interaction, we have propagated a recent isolate (CMV VHL) through multiple passages in human umbilical vein endothelial cells (HUVE) and, collaterally in neonatal human dermal fibroblasts (NHDF). Infection of HUVE inoculated with either sub-strain of the virus was confirmed by CMV-specific in situ hybridization and by immunocytochemical staining for CMV antigens. Whereas infection of HUVE by substrain VHL/E (endothelial-raised) was accompanied by dramatic cytopathology resembling that observed clinically, the endothelial cytopathic potential of VHL/F (fibroblast-raised) was lost by its 20th passage in NHDF. Similarly, the ability of VHL/F to initiate sustained productive infection in HUVE was severely attenuated; plaque assay of culture supernatants and infected cell fractions, as well as virus-specific DNA polymerase assay of cell lysates, demonstrated progressive viral reproductive activity in VHL/E-inoculated HUVE, whereas VHL/F reproduction was barely detectable. Since properties of VHL/F bear strong resemblance to those of the fibroblast-raised AD169, these studies suggest that while the fibroblast adaptation process commonly employed in the propagation of CMV restricts the host range of the virus and attenuates its spectrum of cytopathic potential, endothelial-based propagation preserves the natural endothelial cytopathogenicity of the original isolate.

Characterization of variable regions in the envelope and S3 open reading frame of equine infectious anemia virus

The polymerase chain reaction was used to amplify and clone parts of the envelope gene and overlapping S3 open reading frame, thought to encode rev, of the virulent in vivo-derived Th-1 isolate of equine infectious anemia virus (EIAV). The results indicated that EIAV consists of a heterogeneous mixture of genotypes present at the first febrile cycle after initial infection. We showed that the Th-1 isolate apparently contains nondefective genotypes as well as types which have transmembrane protein truncations or are rev deficient. Furthermore, we could confirm the presence of a hypervariable region in the gp90 envelope glycoprotein. Taken together with earlier data on the heterogeneity of the regulatory motifs present in the long terminal repeat sequences of viruses from the same in vivo isolate (S. Carpenter, S. Alexandersen, M. J. Long, S. Perryman, and B. Chesebro, J. Virol. 65:1605-1610, 1991), our findings indicate that EIAV uses a complex system of diversity in biological phenotypes together with variation in regulatory and antigenic makeup to evade host response and to cause persistent infection and recurrent chronic disease.

Identification of a hypervariable region in the long terminal repeat of equine infectious anemia virus

An avirulent, field-derived isolate of equine infectious anemia virus (EIAV), designated MA-1, was molecularly cloned, and the complete nucleotide sequence was determined for the 3' half of the viral genome. Comparisons between MA-1 and the prototype Wyoming strain of EIAV identified a 66-nucleotide stretch between CAAT (-91) and TATAA (-25) in the U3 region of the long terminal repeat, where sequence divergence was as high as 39.3%. The polymerase chain reaction was used to amplify and clone long terminal repeat sequences from Th-1, the in vivo parental stock of MA-1. Results indicated that the nucleotide sequences of MA-1 and Th-1 clones were less variable than was observed between MA-1 and Wyoming. However, MA-1 and Th-1 markedly differed in the types of enhancer sequences located in the hypervariable region. These results suggest that variation in lentivirus regulatory sequences may be important in EIAV host cell tropism and pathogenesis.

Photosensitization is required for inactivation of equine infectious anemia virus by hypericin

Hypericin, a photoreactive polycyclic quinone, was found to dramatically reduce infectivity of cell-free stocks of equine infectious anemia virus. However, the antiviral activity of hypericin was completely dependent on the presence of light. Short periods of photosensitization resulted in a partial loss of reverse transcriptase activity and complete inhibition of viral infectivity. These results suggest that the photodynamic effect of hypericin interferes with more than one stage in the virus replication cycle.

Equine infectious anemia virus derived from a molecular clone persistently infects horses

A full-length molecular clone of equine infectious anemia virus (EIAV) was isolated from a persistently infected canine fetal thymus cell line (Cf2Th). Upon transfection of equine dermis cells, the clone, designated CL22, yielded infectious EIAV particles (CL22-V) that replicated in vitro in both Cf2Th cells and an equine dermis cell strain. Horses infected with CL22-V developed an antibody response to viral proteins and possessed viral DNA in peripheral blood mononuclear cells, as determined by polymerase chain reaction assays. In addition, horses infected with CL22-V became persistently infected and were capable of transmitting the infection by transfer of whole blood to uninfected horses. However, CL22-V, like the parental canine cell-adapted virus, did not cause clinical signs in infected horses. Reverse transcriptase assays of CL22-V- and virulent EIAV-infected equine mononuclear cell cultures indicated that the lack of virulence of CL22-V was not due to an inability to infect and replicate in equine mononuclear cells in vitro.

Antiretroviral activity of synthetic hypericin and related analogs

Hypericin and pseudohypericin are naturally occurring polycyclic quinones which have recently been shown to inhibit the infectivity of several retroviruses, including human immunodeficiency virus. To better understand the antiviral mechanisms of these compounds, hypericin and a series of analogous quinones were synthesized and tested for anti-retroviral activity against equine infectious anemia virus (EIAV). Treatment of EIAV-infected cells with hypericin reduced the production of infectious virus by 99.99%. None of the analogs were found to inhibit virus replication. These results suggest that the complete ring structure of hypericin is required, but not sufficient, for antiviral activity.

Limited sequence heterogeneity among biologically distinct human immunodeficiency virus type 1 isolates from individuals involved in a clustered infectious outbreak

Human immunodeficiency virus type 1 isolates were obtained over a 3-year period from blood, brain, and lung of three patients in a clustered infectious outbreak. This included a blood donor who was initially asymptomatic but subsequently developed AIDS-related complex and two neonatal transfusion recipients who developed AIDS. Isolates from brain and lung replicated to greater than 30-fold higher levels in primary monocyte cultures than did those from blood; no growth differences on primary lymphocytes were observed. Thirteen clones were obtained from seven isolates, and env sequences were determined. The predicted amino acid sequences among these clones differed by only 0.01% but differed by 15-27% when compared to previously sequenced isolates from other patients. The level of envelope amino acid sequence divergence noted among these isolates is considerably lower than that previously reported for other human immunodeficiency virus isolates. No differences in the envelope unique to lung or brain isolates compared to blood isolates were noted. This study provides evidence that mutations in the envelope may not be necessary for disease progression and that other portions of the viral genome may contribute to cell-specific tropism.