Host receptor-targeted therapeutic approach to counter pathogenic New World mammarenavirus infections

Five New World mammarenaviruses (NWMs) cause life-threatening hemorrhagic fever (HF). Cellular entry by these viruses is mediated by human transferrin receptor 1 (hTfR1). Here, we demonstrate that an antibody (ch128.1/IgG1) which binds the apical domain of hTfR1, potently inhibits infection of attenuated and pathogenic NWMs in vitro. Computational docking of the antibody Fab crystal structure onto the known structure of hTfR1 shows an overlapping receptor-binding region shared by the Fab and the viral envelope glycoprotein GP1 subunit that binds hTfR1, and we demonstrate competitive inhibition of NWM GP1 binding by ch128.1/IgG1 as the principal mechanism of action. Importantly, ch128.1/IgG1 protects hTfR1-expressing transgenic mice against lethal NWM challenge. Additionally, the antibody is well-tolerated and only partially reduces ferritin uptake. Our findings provide the basis for the development of a novel, host receptor-targeted antibody therapeutic broadly applicable to the treatment of HF of NWM etiology.

Novel Dihydroorotate Dehydrogenase Inhibitors with Potent Interferon-Independent Antiviral Activity against Mammarenaviruses In Vitro

Mammarenaviruses cause chronic infections in rodents, which are their predominant natural hosts. Human infection with some of these viruses causes high-consequence disease, posing significant issues in public health. Currently, no FDA-licensed mammarenavirus vaccines are available, and anti-mammarenavirus drugs are limited to an off-label use of ribavirin, which is only partially efficacious and associated with severe side effects. Dihydroorotate dehydrogenase (DHODH) inhibitors, which block de novo pyrimidine biosynthesis, have antiviral activity against viruses from different families, including Arenaviridae, the taxonomic home of mammarenaviruses. Here, we evaluate five novel DHODH inhibitors for their antiviral activity against mammarenaviruses. All tested DHODH inhibitors were potently active against lymphocytic choriomeningitis virus (LCMV) (half-maximal effective concentrations [EC₅₀] in the low nanomolar range, selectivity index [SI] > 1000). The tested DHODH inhibitors did not affect virion cell entry or budding, but rather interfered with viral RNA synthesis. This interference resulted in a potent interferon-independent inhibition of mammarenavirus multiplication in vitro, including the highly virulent Lassa and Junín viruses.

Antibody response in snakes with boid inclusion body disease

Boid Inclusion Body Disease (BIBD) is a potentially fatal disease reported in captive boid snakes worldwide that is caused by reptarenavirus infection. Although the detection of intracytoplasmic inclusion bodies (IB) in blood cells serves as the gold standard for the ante mortem diagnosis of BIBD, the mechanisms underlying IB formation and the pathogenesis of BIBD are unknown. Knowledge on the reptile immune system is sparse compared to the mammalian counterpart, and in particular the response towards reptarenavirus infection is practically unknown. Herein, we investigated a breeding collection of 70 Boa constrictor snakes for BIBD, reptarenavirus viraemia, anti-reptarenavirus IgM and IgY antibodies, and population parameters. Using NGS and RT-PCR on pooled blood samples of snakes with and without BIBD, we could identify three different reptarenavirus S segments in the collection. The examination of individual samples by RT-PCR indicated that the presence of University of Giessen virus (UGV)-like S segment strongly correlates with IB formation. We could also demonstrate a negative correlation between BIBD and the presence of anti-UGV NP IgY antibodies. Further evidence of an association between antibody response and BIBD is the finding that the level of anti-reptarenavirus antibodies measured by ELISA was lower in snakes with BIBD. Furthermore, female snakes had a significantly lower body weight when they had BIBD. Taken together our findings suggest that the detection of the UGV-/S6-like S segment and the presence of anti-reptarenavirus IgY antibodies might serve as a prognostic tool for predicting the development of BIBD.

Interactome analysis of the lymphocytic choriomeningitis virus nucleoprotein in infected cells reveals ATPase Na+/K+ transporting subunit Alpha 1 and prohibitin as host-cell factors involved in the life cycle of mammarenaviruses

Several mammalian arenaviruses (mammarenaviruses) cause hemorrhagic fevers in humans and pose serious public health concerns in their endemic regions. Additionally, mounting evidence indicates that the worldwide-distributed, prototypic mammarenavirus, lymphocytic choriomeningitis virus (LCMV), is a neglected human pathogen of clinical significance. Concerns about human-pathogenic mammarenaviruses are exacerbated by of the lack of licensed vaccines, and current anti-mammarenavirus therapy is limited to off-label use of ribavirin that is only partially effective. Detailed understanding of virus/host-cell interactions may facilitate the development of novel anti-mammarenavirus strategies by targeting components of the host-cell machinery that are required for efficient virus multiplication. Here we document the generation of a recombinant LCMV encoding a nucleoprotein (NP) containing an affinity tag (rLCMV/Strep-NP) and its use to capture the NP-interactome in infected cells. Our proteomic approach combined with genetics and pharmacological validation assays identified ATPase Na⁺/K⁺ transporting subunit alpha 1 (ATP1A1) and prohibitin (PHB) as pro-viral factors. Cell-based assays revealed that ATP1A1 and PHB are involved in different steps of the virus life cycle. Accordingly, we observed a synergistic inhibitory effect on LCMV multiplication with a combination of ATP1A1 and PHB inhibitors. We show that ATP1A1 inhibitors suppress multiplication of Lassa virus and Candid#1, a live-attenuated vaccine strain of Junín virus, suggesting that the requirement of ATP1A1 in virus multiplication is conserved among genetically distantly related mammarenaviruses. Our findings suggest that clinically approved inhibitors of ATP1A1, like digoxin, could be repurposed to treat infections by mammarenaviruses pathogenic for humans.

Viral hemorrhagic fever-causing mammalian viruses of the family Arenaviridae pose serious threats to humans in Africa and South America as the associated infections are highly lethal. The worldwide-distributed lymphocytic choriomeningitis virus (LCMV) is a relative of these dangerous viruses that can be worked with more safely in the laboratory. Although LCMV does not cause viral hemorrhagic fever, it can cause disease in humans. Currently, anti-arenavirus therapy options are very limited, not very effective, and associated with side effects. Development of new therapies has been hampered because knowledge on how arenaviruses interact with proteins of the host cells they infect is limited. Using a modified LCMV, we identified two host-cell proteins called ATPase Na+/K+ transporting subunit alpha 1 (ATP1A1) and prohibitin (PHB) as factors that promote arenavirus infection. Inhibitors of ATP1A1 (cardiac glycosides already used clinically for treatment of other diseases) suppressed multiplication in cell culture of Lassa virus and Junín virus, the two most significant viral hemorrhagic fever-causing mammarenaviruses. Therefore, our data suggest that these inhibitors could be used clinically to treat people infected with arenaviruses.

Minigenomes, transcription and replication competent virus-like particles and beyond: reverse genetics systems for filoviruses and other negative stranded hemorrhagic fever viruses

Reverse-genetics systems are powerful tools enabling researchers to study the replication cycle of RNA viruses, including filoviruses and other hemorrhagic fever viruses, as well as to discover new antivirals. They include full-length clone systems as well as a number of life cycle modeling systems. Full-length clone systems allow for the generation of infectious, recombinant viruses, and thus are an important tool for studying the virus replication cycle in its entirety. In contrast, life cycle modeling systems such as minigenome and transcription and replication competent virus-like particle systems can be used to simulate and dissect parts of the virus life cycle outside of containment facilities. Minigenome systems are used to model viral genome replication and transcription, whereas transcription and replication competent virus-like particle systems also model morphogenesis and budding as well as infection of target cells. As such, these modeling systems have tremendous potential to further the discovery and screening of new antivirals targeting hemorrhagic fever viruses. This review provides an overview of currently established reverse genetics systems for hemorrhagic fever-causing negative-sense RNA viruses, with a particular emphasis on filoviruses, and the potential application of these systems for antiviral research.

Posttranslational modification of alpha-dystroglycan, the cellular receptor for arenaviruses, by the glycosyltransferase LARGE is critical for virus binding

The receptor for lymphocytic choriomeningitis virus (LCMV), the human pathogenic Lassa fever virus (LFV), and clade C New World arenaviruses is alpha-dystroglycan (alpha-DG), a cell surface receptor for proteins of the extracellular matrix (ECM). Specific posttranslational modification of alpha-DG by the glycosyltransferase LARGE is critical for its function as an ECM receptor. In the present study, we show that LARGE-dependent modification is also crucial for alpha-DG's function as a cellular receptor for arenaviruses. Virus binding involves the mucin-type domain of alpha-DG and depends on modification by LARGE. A crucial role of the LARGE-dependent glycosylation of alpha-DG for virus binding is found for several isolates of LCMV, LFV, and the arenaviruses Mobala and Oliveros. Since the posttranslational modification by LARGE is crucial for alpha-DG recognition by both arenaviruses and the host-derived ligand laminin, it also influences competition between virus and laminin for alpha-DG. Hence, LARGE-dependent glycosylation of alpha-DG has important implications for the virus-host cell interaction and the pathogenesis of LFV in humans.

Dengue y otras fiebres hemorrágicas virales

Few diseases generate such alarm among the general population and health professionals as viral hemorrhagic fevers (VHFs). VHFs are acute infections with high associated mortality that are difficult to clinically diagnose and differentiate. Reliable laboratory diagnosis is required for proper patient support and to limit the risk of transmission and the development of secondary cases. Even today many factors related to origin, pathogenesis, treatment and control of these diseases remain uncertain.

Lassa and Mopeia virus replication in human monocytes/macrophages and in endothelial cells: different effects on IL-8 and TNF-alpha gene expression

Cells of the mononuclear and endothelial lineages are targets for viruses which cause hemorrhagic fevers (HF) such as the filoviruses Marburg and Ebola, and the arenaviruses Lassa and Junin. A recent model of Marburg HF pathogenesis proposes that virus directly causes endothelial cell damage and macrophage release of TNF-alpha which increases the permeability of endothelial monolayers [Feldmann et al. , 1996]. We show that Lassa virus replicates in human monocytes/macrophages and endothelial cells without damaging them. Human endothelial cells (HUVEC) are highly susceptible to infection by both Lassa and Mopeia (a non-pathogenic Lassa-related arenavirus). Whereas monocytes must differentiate into macrophages before supporting even low level production of these viruses, the virus yields in the culture medium of infected HUVEC cells reach more than 7 log10 PFU/ml without cellular damage. In contrast to filovirus, Lassa virus replication in monocytes/macrophages fails to stimulate TNF-alpha gene expression and even down-regulates LPS-stimulated TNF-alpha mRNA synthesis. The expression of IL-8, a prototypic proinflammatory CXC chemokine, was also suppressed in Lassa virus infected monocytes/macrophages and HUVEC on both the protein and mRNA levels. This contrasts with Mopeia virus infection of HUVEC in which neither IL-8 mRNA nor protein are reduced. The cumulative down-regulation of TNF-alpha and IL-8 expression could explain the absence of inflammatory and effective immune responses in severe cases of Lassa HF.

Pathogenesis of Pichinde virus infection in strain 13 guinea pigs: an immunocytochemical, virologic, and clinical chemistry study

Pichinde virus has been adapted to produce lethal infection of Strain 13 guinea pigs. Viral replication and presence of viral antigen in frozen tissues stained by immunofluorescence has been previously described. Further investigation into the pathogenesis of this disease has been hampered by the lack of a light microscopic method for correlating histologic lesions and the presence of Pichinde viral antigens. For this purpose, we developed a sensitive immunocytochemical technique for staining Pichinde viral antigens in formalin-fixed, paraffin-embedded tissue. Enhancement of the immunocytochemical staining with nickel chloride markedly improved detection of viral antigens. We examined frozen and formalin-fixed tissues from Strain 13 guinea pigs for viral antigens by light microscopy and immunocytochemistry at various intervals after infection with Pichinde virus. Progressive involvement of different tissues correlated with organ injury measured by serum biochemical abnormalities. Pichinde viral antigen was first detected in splenic macrophages five days after infection and their subsequent destruction facilitated persistent viremia. The inability to clear virus led to multiple organ infection and vascular involvement. Ensuing infections involved particularly the liver, spleen, adrenal glands, lungs, and intestines. Gastroenteritis developed, with extensive involvement of the muscularis mucosa throughout the gastrointestinal tract. Water and food intake decreased rapidly after day 8, leading to marked weight loss. Fatty changes of the liver suggested metabolic derangement that was further exacerbated terminally by adrenal infection and pulmonary impairment.

Isolation of an arenavirus from a marmoset with callitrichid hepatitis and its serologic association with disease

Callitrichid hepatitis (CH) is an acute, often fatal viral infection of New World primates from the family Callitrichidae. The etiologic agent of CH is unknown. We report here the isolation of an arenavirus from a common marmoset (Callithrix jacchus) with CH by using in vitro cultures of marmoset hepatocytes and Vero-E6 cells. Enveloped virions 67 to 133 nm in diameter with ribosomelike internal structures were seen in infected cultures. Immunofluorescence and Western immunoblot analysis using CH-specific antisera (principally from animals exposed to CH during zoo outbreaks) revealed three antigens in cells infected with this CH-associated virus (CHV). These antigens had the same electrophoretic mobilities on sodium dodecyl sulfate-polyacrylamide gels as did the nucleocapsid, GP2, and GPC proteins of lymphocytic choriomeningitis virus (LCMV). Monoclonal antibodies specific for these arenavirus proteins also reacted with the three CHV antigens. Conversely, the CH-specific antisera reacted with the nucleocapsid, GP2, and GPC proteins of LCMV. CHV thus appears to be a close antigenic relative of LCMV. The serologic association of CHV with several CH outbreaks implicate it as the etiologic agent of this disease.

[Lysosomotropic agents inhibit the penetration of arenaviruses into a culture of BHK-21 and Vero cells]

Lysosomotropic agents (NH4Cl, amantadine, chloroquine, monensin) which prevent acidification of intracellular vacuoles, when introduced into the culture medium before or during inoculation of cells (BHK-21, Vero) with arenaviruses inhibit reproduction of these viruses completely or significantly. Mozambique virus proved to be 10 times more sensitive to the effect of lysosomotropic agents than Pichinde and Lassa viruses. Thus, arenaviruses have a pH-dependent stage at the beginning of the reproduction cycle which is indirectly indicative of their penetration into cells by receptor endocytosis.

Replication of hemorrhagic fever viruses in monocytic cells

Monocytes play a central role in protection against many viruses. In some infections they are target cells for viral replication. There is increasing evidence that these cells may also be important in regulation of hemostasis. The part played by monocytic cells in the pathogenesis of hemorrhage in the viral hemorrhagic fevers is presently uncertain. Monocytes and monocytic cell lines have been used to investigate the ability of viruses to infect these cells in vitro. Several factors may affect the ability of a particular virus to infect monocytic cells, including specific antiserum to virus and the degree of cellular maturation. The effect of cellular maturation on the replication of Rift Valley fever virus in the U937 cell line is discussed in light of studies on the infectivity of other viruses for monocytic cells. Data supporting the ability of specific antibody to enhance the infectivity of Pichinde virus and Lassa fever virus for U937 cells are presented.

Early events in arenavirus replication are sensitive to lysosomotropic compounds

Lysosomotropic compounds (ammonium chloride, chloroquine, amantadine, monensin) effectively inhibited the replication of Pichinde, Mopeia, and Lassa viruses in BHK-21 and Vero cells. The inhibitory effect was dependent upon the time of drug addition and was most effective when the drugs were added 1 h before the viral adsorption. The drugs had no direct effect on the infectious viruses nor on adsorption of the arenaviruses. These results suggest that the arenaviruses enter cells by adsorptive endocytosis with the participation of acidic intracellular vesicules.

Immune serum increases arenavirus replication in monocytes

The U937 monocytic cell line was used to determine whether antibodies could facilitate infection and replication of the arenaviruses, Pichinde virus (PV) and Lassa fever virus (LFV). When high dilutions of PV-immune serum were added to cultures simultaneously with PV inoculum, virus replication was dramatically (1000-fold) increased. Low dilutions of this antiserum neutralized the virus. LFV also replicated in U937 cells. The presence of LFV-specific immune serum in the growth medium increased the viral titre as much as 10,000-fold. Addition of heat-aggregated IgG partially inhibited antibody-mediated enhancement, probably by inhibiting the binding of immune complexes to the monocytic cells.

Tacaribe virus infection may induce inhibition of the activity of the host cell Ca2+ and Na+/K+ pumps

Infection of Vero cells with Tacaribe virus stocks containing a high ratio of standard (plaque-forming) viruses to defective interfering particles (DIP) induced inhibition of the host cell Ca2+ ATPase (Ca2+ pump) and the ouabain-sensitive Na+/K+ ATPase (Na+/K+ pump). The Mg2+ ATPase which is not involved in cation transport was not affected. The presence of DIP in the inocula protected the cells from alteration of the transport-associated ATPases induced by standard viruses.

Virus-specific factors in experimental Argentine hemorrhagic fever in rhesus macaques

A nonhuman primate model for Argentine hemorrhagic fever has been developed that closely mimics the human clinical syndrome. Parenteral infection of adult Macaca mulatta with low-passage isolates of two Junin viral strains resulted in distinctive hemorrhagic or neurological disease in rhesus macaques that correlated with clinical illness patterns present in the humans from whom the viral strains were obtained. Transient leukopenia, together with thrombocytopenia and secondary bacterial septicemia, were documented among animals infected with both viral strains. In contrast, differing patterns of viremia, oropharyngeal viral shedding, and antibody response occurred in the two virus-infected groups. These results, together with postmortem virologic and histopathologic findings, suggest that viral-strain-specific factors are important determinants of clinical disease patterns in this model system.

Molecular structure and early events in the replication of Tacaribe arenavirus S RNA

Tacaribe arenavirus S RNA was cloned and analysis of its nucleotide sequence revealed two open reading frames of significant size, one in the virus-sense strand, the other in the virus-complementary strand. The predicted amino acid sequences of the two reading frames were compared with the predicted primary structures of the nucleoprotein (N) and glycoprotein precursor (GPC) of LCM, Pichinde and Lassa viruses. The results indicated a high degree of homology between the proteins of similar properties. It was also found that in Tacaribe virus-infected cells a subgenomic viral-sense GPC RNA and a subgenomic viral-complementary N RNA are synthesized in addition to the full length viral (v) RNA and viral complementary (vc) RNAs. These results support the conclusion that in Tacaribe virus--as in Pichinde and lymphocytic choriomeningitis arenavirus-S RNA encodes the viral N and GPC proteins and has an 'ambisense' coding strategy. Analysis of the S-derived RNA species at early times post-infection in cells incubated with or without inhibitors of protein synthesis indicated that for primary transcription of the N mRNA, protein synthesis is not required; whereas synthesis of the vc RNA, GPC mRNA and v RNA does require protein synthesis to take place.

Macrophages are involved in age-dependent resistance of rats to Junin virus infection

We attempted to correlate rat age with resistance to intraperitoneal infection with the XJ strain of Junin virus. Accordingly, mortality, viral replication in macrophages and brain, as well as neutralizing antibody (NA) levels were recorded in animals inoculated at 2, 5, 10 and 26 days of life. Two-day-old animals demonstrated both the greatest mortality (86%) and viral replication in macrophages, allowing virus to reach the brain where high titers were detected. This age group also had the highest NA titers. Mortality, viral multiplication and NA titers diminished with increasing age of the animals. The ability of peritoneal macrophages to support viral replication, therefore, seems to determine rat susceptibility to intraperitoneal infection with Junin virus.

Vero cells persistently infected with Tacaribe virus: role of interfering particles in the establishment of the infection

Eight Vero cell sublines (Vero T) persistently infected with wild type Tacaribe virus replicated in different hosts were established. In order to unravel the mechanism involved in the initiation and maintenance of persistence, the properties of virus shed by the sublines and the presence of interfering particles (IP) were analyzed. During the course of infection, persistent virus (Tac-pi) underwent mutations although no consistent pattern of virus evolution was observed. ts mutants were isolated from two Vero T sublines, whereas a slow growth variant was shed by another. The remaining sublines released virus resembling wt parental virus. Except for Vero T1 sublines, Vero T cultures shed no detectable IP. These results emphasize the point that neither the emergence of virus mutants nor the synthesis of IP is essential for the maintenance of the persistent state. To define the role of IP in the initiation of persistence, coinfection experiments with a characterized inoculum were performed. For that purpose, attempts were made to obtain IP stocks free from pfu by serial transfers of undiluted virus. Neither enrichment nor amplification of IP occurred, and virus stocks were freed of infectious virus by UV irradiation. If normal Vero cells were infected with Tac-pi virus released by Vero T2, Vero T3, Vero T4, Vero T5, Vero T6, Vero T7 and Vero T10 sublines, a complete destruction of the monolayer without cell recovery was observed. In contrast, parental and Vero T1 viruses always originated persistently infected sublines. Similarly, the addition of IP to virus inocula constituted by Tac-pi viruses released by Vero T2, Vero T3, Vero T4, Vero T5, Vero T6, Vero T7 and Vero T10 sublines gave rise to persistently infected cultures. These results suggest that although IP are not important by themselves in the maintenance of persistence, they play a major role in initiation.

Ambisense RNA genomes of arenaviruses and phleboviruses

This chapter reviews the evidence that shows that arenaviruses and members of one genus of the Bunyaviridae (phleboviruses) have some proteins coded in subgenomic, viral-sense mRNA species and other proteins coded in subgenomic, viral-complementary mRNA sequences. This unique feature is discussed in relation to the implications it has on the intracellular infection process and how such a coding arrangement may have evolved. The chapter presents a list of the known members of the arenaviridae, their origins, and the vertebrate hosts from which isolates have been reported. It discusses the structural components, the infection cycle, and genetic attributes of arenaviruses. In order to determine how arenaviruses code for gene products, the S RNA species of Pichinde virus and that of a viscerotropic strain of LCM virus (LCM-WE) have been cloned into DNA and sequenced. The arenavirus S RNA is described as having an ambisense strategy, to denote the fact that both viral and viral-complementary sequences are used to make gene products. The chapter discusses the infection cycle, the structural and genetic properties of bunyaviridae member.

Thermal inactivation of Pichinde virus

Detailed information regarding the kinetics of thermal inactivation of Pichinde, an arenavirus, is presented. Inactivation of virus infectivity proceeded as a first order reaction over the temperature range 22-53 degrees C. The determined inactivation rates analysed as a function of absolute temperature revealed that two different reactions were involved. Below 37 degrees C, the energy of activation was determined to be compatible with RNA degradation, whereas at higher temperatures a correspondingly greater value suggests that protein inactivation contributes significantly to loss of infectivity. Both inactivation reactions were retarded in the presence of foetal calf serum to a final concentration of 1%. The relatively short half-life of 12-24 h at 22 degrees C suggests transmission in nature via contaminated foodstuffs and soil may be inefficient.

MRC-5 cells, a model for Junín virus persistent infection

Persistent infection of MRC-5 cells was established following inoculation with attenuated Junín virus (JV). In the acute phase of the infection both the pathogenic XJ and the attenuated XJ0 and XJC13 strains showed severe c.p.e. and free viral titres reached 10(5) p.f.u./ml. Recovery and establishment of persistently infected MRC-5 sublines (MRC-5PI) proved a very common event and seemed to be independent of viral strain, m.o.i. employed or virus passage history. These MRC-5PI sublines released virus throughout their life span and infectious centre assays performed at different passage levels with two sublines showed that 5 to 9% of the cells were producing virus. Heterotypic but not heterologous resistance to superinfection developed, as observed in persistent JV-heteroploid cell systems. Analysis of released JV showed that attenuation had not been markedly altered, but alteration in plaque morphology under methyl cellulose, appearance of temperature-sensitive mutants and alterations in mouse pathology imply that some properties of JV have been altered. Results presented here stress once again the ability of JV to establish persistent infections. The source and diploid characteristics of MRC-5 cells make them a satisfactory model for JV persistence studies.

Interactions of Junin and Tacaribe viruses during mixed infections

The interaction between Junin virus (JV) and Tacaribe virus (TACV) during mixed infections of RK13 cells was examined. The effects of a prior infection with JV upon TACV replication depended on the time between the two inoculations. Simultaneous infection of RK13 cells with TACV and JV did not alter the plaquing efficiency of TACV; but if there was a 1- to 24-hour delay between JV preinfection and TACV superinfection, a variable increase of TACV replication was observed. The enhancement of TACV replication by preinfection with JV was dependent on several factors, such as the MOI of both viruses and the integrity of the JV genome. This effect was also highly specific, as the plaquing efficiencies of the arenavirus Pichinde and the unrelated vesicular stomatitis virus were not affected by preinfection with JV at any multiplicity assayed. The majority of the progeny formed in cells superinfected with TACV 1 or 24 h after JV infection was partially neutralized by antisera to both viruses. This suggested that phenotypic mixing, with JV or TACV genomes enclosed within an envelope containing TACV and JV glycoprotein, had occurred.

Junin virus-induced chromosomal aberrations in the guinea pig. Synergism between the attenuated strain XJ-clone 3 and caffeine

The frequency of chromosomal aberrations in bone marrow cells of guinea pigs inoculated with the pathogenic XJ strain of Junin virus increased significantly at 6, 9, and 11 days postinoculation (p.i.). Animals inoculated with the attenuated XJ-clone 3 strain only showed significant increments of achromatic lesions (gaps) at 9 days p.i. Guinea pigs inoculated with the XJ-clone 3 strain and then treated with two doses of caffeine 24 and 12 h before killing at 9 days p.i. exhibited a significant increase of chromatid breaks and a parallel decrease of gaps. Because caffeine acts as an inhibitor of repair mechanisms of genetic damage, these results suggest a mutagenic effect of the attenuated strain.

Replication of Junin virus in the presence of tunicamycin

In the presence of tunicamycin (TM), an antibiotic which inhibits glycosylation, Junin virus-infected cells released 70% as much virus as control cultures, as measured by [35S]-methionine appearing in a sucrose gradient virus particle fraction. In this same fraction, the incorporation of [14C]-glucosamine was inhibited 85% by TM, accompanied by a dramatic decrease in the envelope glycoprotein, Gp38, and a marked decrease in virus infectivity. These results indicate that the presence of Gp38 on the viral surface is essential for viral infectivity. In contrast, maturation and release of virus particles do not seem to be affected by the absence of Gp38 from the viral envelope.

Response of cells persistently infected with arenaviruses to superinfection with homotypic and heterotypic viruses

Vero cell cultures persistently infected with the arenaviruses Junin, Pichinde, Tacaribe, and Tamiami were established and designated Vero-Jun, Vero-Pic, Vero-Tac, and Vero-Tam, respectively. Two types of carrier cultures could be easily distinguished: Vero-Jun and Vero-Tac systems were characterized by a lack of infectious virus production after a few cell transfers, whereas a more productive state with continuous release of virus was observed in Vero-Pic and Vero-Tam cultures. These differences appeared to be related to resistance of the culture to viral superinfection. In fact, Vero-Jun and Vero-Tac cultures totally excluded only the replication of the serologically more closely related arenaviruses Amapari, Junin, or Tacaribe, while the refractoriness of Vero-Pic and Vero-Tam cultures was extended to most of the virus group members. The resistance of Vero-Jun cells to superinfection by Junin or Tacaribe virus could be ascribed to the production of specific uv-resistant Junin interfering particles, which showed a specific range of interference against Junin and Tacaribe viruses. Interfering particles against homotypic and heterotypic arenaviruses were isolated from Vero-Pic cultures. However, the degree of interference developed by these Pic-interfering particles was not enough to fully explain reinfecting virus exclusion from Vero-Pic cultures. Viral susceptibility of persistent cultures is proposed as a useful tool to examine relationships of members of the arenavirus group.

In vivo replication of pathogenic and attenuated strains of Junin virus in different cell populations of lymphatic tissue

Lymphatic tissue is one of the main sites for replication of Junin virus. To characterize which cells are involved in that replication, the presence of Junin virus in purified populations of macrophages and dendritic cells from the spleens of guinea pigs infected with pathogenic and attenuated strains was investigated by immunofluorescence and intracerebral inoculation into newborn mice. The pathogenic strain was present both in macrophages and in dendritic cells, but the attenuated strain selectively infected dendritic cells. These observations suggest that the pathogenic behavior and replication efficiency of these two strains of Junin virus may be related to a difference in cell targets.

New attenuation marker for junin virus based on immunologic responses of guinea pigs

A new attenuation marker to distinguish a virulent strain (XJJV) from an attenuated strain (XJC13JV or XJOJV) of Junin virus by means of the humoral and cellular responses to unrelated antigens was studied in guinea pigs. Strain XJJV suppressed the humoral immune response, as shown by the lower titers of precipitating antibody to ovalbumin. The concomitant decrease in serum complement level contributed to a milder Arthus cutaneous reactivity. In contrast, the attenuated strains did not decrease the humoral response. The pathogenic strain suppressed cell-mediated immunity, as demonstrated by decreased contact sensitivity to 2,4-dinitro-1-fluorobenzene and by depression of delayed skin reactions to tuberculin purified protein derivative. When attenuated strains were used, such suppressive effects were not observed. For virulent strain XJJV, virus replication in lymphoid organs and immunosuppressive effects were correlated. These findings provide a further means to differentiate between virulent and attenuated strains of Junin virus for the purpose of vaccine control of Argentine hemorrhagic fever.

Mechanisms of persistence in arenavirus infections: a brief review

A characteristic of the arenaviruses is persistent infections in their natural host. Age at infection is an important factor in the establishment of persistence. Infections early in life regularly result in persistence and this appears to be related to the immaturity of the immune system. Persistently infected animals make antibodies to the viral antigens, which indicates that the animals are not tolerant with respect to B cell functions. However, cytotoxic T cells cannot be demonstrated in persistently infected animals, suggesting a defect in effector T cell functions. The mechanisms leading to this defect in cytotoxic T cells have not been resolved. Persistence of arenaviruses in cell cultures is also regularly observed but the molecular basis for survival of the virus and cell in long-term cultures has yet to be clarified.

[Optimal conditions for preserving the infectivity of Tacaribe virus under various temperatures]

The stability of Tacaribe virus at different temperatures and the stabilizing effect of calf serum or human albumin were studied. The viral stock employed in this study was a 10% suckling mouse brain suspension prepared in phosphate buffer saline and fractionated in three aliquots: the first was supplemented with 0.5% human albumin, the second with 5% calf serum and the third was maintained without stabilizing agent. The infectivity of Tacaribe virus kept at -70 degrees C was preserved during several months and the reduction in infectivity was not significant even if the viral sample was frozen and thawed four times. However, the addition of an stabilizing protein to the viral stock was necessary to maintain it at -16 or 4 degrees C. Under these conditions, the viral infectivity was completely lost after 3 days when the stock was prepared in phosphate buffer saline alone, while more than 40 days were necessary to destroy the infectivity in presence of serum or albumin. The viral inactivation was completed after 48 hours at 25 or 37 degrees C or 10 minutes at 56 degrees C.

[Inhibition of the multiplication of Tacaribe, Pichindé and Junín arenaviruses in the presence of glucosamine or 2-deoxy-D-glucose]

The multiplication of arenaviruses Tacaribe, Pichinde and Junin was inhibited by 16 mM of glucosamine and by 10 mM of 2-deoxi-D-glucose.