Viremia In Mice Research Articles

Mechanisms of Flavivirus Cross-Protection against Yellow Fever in a Mouse Model.

The complete lack of yellow fever virus (YFV) in Asia, and the lack of urban YFV transmission in South America, despite the abundance of the peridomestic mosquito vector Aedes (Stegomyia.) aegypti is an enigma. An immunologically naïve population of over 2 billion resides in Asia, with most regions infested with the urban YF vector. One hypothesis for the lack of Asian YF, and absence of urban YF in the Americas for over 80 years, is that prior immunity to related flaviviruses like dengue (DENV) or Zika virus (ZIKV) modulates YFV infection and transmission dynamics. Here we utilized an interferon α/β receptor knock-out mouse model to determine the role of pre-existing dengue-2 (DENV-2) and Zika virus (ZIKV) immunity in YF virus infection, and to determine mechanisms of cross-protection. We utilized African and Brazilian YF strains and found that DENV-2 and ZIKV immunity significantly suppresses YFV viremia in mice, but may or may not protect relative to disease outcomes. Cross-protection appears to be mediated mainly by humoral immune responses. These studies underscore the importance of re-assessing the risks associated with YF outbreak while accounting for prior immunity from flaviviruses that are endemic.

The in vitro and in vivo antiviral effects of aloperine against Zika virus infection

AbstractZika virus (ZIKV) infection poses a significant threat to global public health and is associated with microcephaly. There are no approved ZIKV‐specific vaccines or drugs for the clinical treatment of the infection. Currently, there are no approved ZIKV‐specific vaccines or drugs for the clinical treatment of the infection. In this study, we investigated the antiviral potential of aloperine, a quinolizidine alkaloid, against ZIKV infection in vivo and in vitro. Our results demonstrate that aloperine effectively inhibits ZIKV infection in vitro, with a low nanomolar half maximal effective concentration (EC50). Specifically, aloperine strongly protected cells from ZIKV multiplication, as indicated by decreased expression of viral proteins and virus titer. Our further investigations using the time‐of‐drug‐addition assay, binding, entry, and replication assays, detection of ZIKV strand‐specific RNA, the cellular thermal shift assay, and molecular docking revealed that aloperine significantly inhibits the replication stage of the ZIKV life cycle by targeting the domain RNA‐dependent RNA polymerase (RDRP) of ZIKV NS5 protein. Additionally, aloperine reduced viremia in mice and effectively lowered the mortality rate in infected mice. These findings highlight the potency of aloperine and its ability to target ZIKV infection, suggesting its potential as a promising antiviral drug against ZIKV.

Chimeric Virus-like Particle-Based COVID-19 Vaccine Confers Strong Protection against SARS-CoV-2 Viremia in K18-hACE2 Mice.

Virus-like particles (VLPs) are highly immunogenic and versatile subunit vaccines composed of multimeric viral proteins that mimic the whole virus but lack genetic material. Due to the lack of infectivity, VLPs are being developed as safe and effective vaccines against various infectious diseases. In this study, we generated a chimeric VLP-based COVID-19 vaccine stably produced by HEK293T cells. The chimeric VLPs contain the influenza virus A matrix (M1) proteins and the SARS-CoV-2 Wuhan strain spike (S) proteins with a deletion of the polybasic furin cleavage motif and a replacement of the transmembrane and cytoplasmic tail with that of the influenza virus hemagglutinin (HA). These resulting chimeric S-M1 VLPs, displaying S and M1, were observed to be enveloped particles that are heterogeneous in shape and size. The intramuscular vaccination of BALB/c mice in a prime-boost regimen elicited high titers of S-specific IgG and neutralizing antibodies. After immunization and a challenge with SARS-CoV-2 in K18-hACE2 mice, the S-M1 VLP vaccination resulted in a drastic reduction in viremia, as well as a decreased viral load in the lungs and improved survival rates compared to the control mice. Balanced Th1 and Th2 responses of activated S-specific T-cells were observed. Moderate degrees of inflammation and viral RNA in the lungs and brains were observed in the vaccinated group; however, brain lesion scores were less than in the PBS control. Overall, we demonstrate the immunogenicity of a chimeric VLP-based COVID-19 vaccine which confers strong protection against SARS-CoV-2 viremia in mice.

The viral distribution and pathological characteristics of BALB/c mice infected with highly pathogenic Influenza H7N9 virus

BackgroundThe highly pathogenic Influenza H7N9 virus is believed to cause multiple organ infections. However, there have been few systematic animal experiments demonstrating the virus distribution after H7N9 virus infection. The present study was carried out to investigate the viral distribution and pathological changes in the main organs of mice after experimental infection with highly pathogenic H7N9 virus.MethodsInfection of mice with A/Guangdong/GZ8H002/2017(H7N9) virus was achieved via nasal inoculation. Mice were killed at 2, 3, and 7 days post infection. The other mice were used to observe their illness status and weight changes. Reverse transcription polymerase chain reaction and viral isolation were used to analyse the characteristics of viral invasion. The pathological changes of the main organs were observed using haematoxylin and eosin staining and immunohistochemistry.ResultsThe weight of H7N9 virus-infected mice increased slightly in the first two days. However, the weight of the mice decreased sharply in the following days, by up to 20%. All the mice had died by the 8th day post infection and showed multiple organ injury. The emergence of viremia in mice was synchronous with lung infection. On the third day post infection, except in the brain, the virus could be isolated from all organs (lung, heart, kidney, liver, and spleen). On the seventh day post infection, the virus could be detected in all six organs. Brain infection was detected in all mice, and the viral titre in the heart, kidney, and spleen infection was high.ConclusionAcute diffuse lung injury was the initial pathogenesis in highly pathogenic H7N9 virus infection. In addition to lung infection and viremia, the highly pathogenic H7N9 virus could cause multiple organ infection and injury.

A Recombinant Subunit Based Zika Virus Vaccine Is Efficacious in Non-human Primates.

Zika Virus (ZIKV), a virus with no severe clinical symptoms or sequelae previously associated with human infection, became a public health threat following an epidemic in French Polynesia 2013–2014 that resulted in neurological complications associated with infection. Although no treatment currently exists, several vaccines using different platforms are in clinical development. These include nucleic acid vaccines based on the prM-E protein from the virus and purified formalin-inactivated ZIKV vaccines (ZPIV) which are in Phase 1/2 clinical trials. Using a recombinant subunit platform consisting of antigens produced in Drosophila melanogaster S2 cells, we have previously shown seroconversion and protection against viremia in an immunocompetent mouse model. Here we demonstrate the efficacy of our recombinant subunits in a non-human primate (NHP) viremia model. High neutralizing antibody titers were seen in all protected macaques and passive transfer demonstrated that plasma from these NHPs was sufficient to protect against viremia in mice subsequently infected with ZIKV. Taken together our data demonstrate the immunogenicity and protective efficacy of the recombinant subunit vaccine candidate in NHPs as well as highlight the importance of neutralizing antibodies in protection against ZIKV infection and their potential implication as a correlate of protection.

Protective Capacity of the Human Anamnestic Antibody Response during Acute Dengue Virus Infection

ABSTRACTHalf of the world's population is exposed to the risk of dengue virus infection. Although a vaccine for dengue virus is now available in a few countries, its reported overall efficacy of about 60% is not ideal. Protective immune correlates following natural dengue virus infection remain undefined, which makes it difficult to predict the efficacy of new vaccines. In this study, we address the protective capacity of dengue virus-specific antibodies that are produced by plasmablasts a few days after natural secondary infection. Among a panel of 18 dengue virus-reactive human monoclonal antibodies, four groups of antibodies were identified based on their binding properties. While antibodies targeting the fusion loop of the glycoprotein of dengue virus dominated the antibody response, two smaller groups of antibodies bound to previously undescribed epitopes in domain II of the E protein. The latter, largely serotype-cross-reactive antibodies, demonstrated increased stability of binding at pH 5. These antibodies possessed weak to moderate neutralization capacity in vitro but were the most efficacious in promoting the survival of infected mice. Our data suggest that the cross-reactive anamnestic antibody response has a protective capacity despite moderate neutralization in vitro and a moderate decrease of viremia in vivo.IMPORTANCE Antibodies can protect from symptomatic dengue virus infection. However, it is not easy to assess which classes of antibodies provide protection because in vitro assays are not always predictive of in vivo protection. During a repeat infection, dengue virus-specific immune memory cells are reactivated and large amounts of antibodies are produced. By studying antibodies cloned from patients with heterologous secondary infection, we tested the protective value of the serotype-cross-reactive “recall” or “anamnestic” response. We found that results from in vitro neutralization assays did not always correlate with the ability of the antibodies to reduce viremia in a mouse model. In addition, a decrease of viremia in mice did not necessarily improve survival. The most protective antibodies were stable at pH 5, suggesting that antibody binding in the endosomes, after the antibody-virus complex is internalized, might be important to block virus spread in the organism.

Ability of the Encephalitic Arbovirus Semliki Forest Virus To Cross the Blood-Brain Barrier Is Determined by the Charge of the E2 Glycoprotein.

ABSTRACTSemliki Forest virus (SFV) provides a well-characterized model system to study the pathogenesis of virus encephalitis. Several studies have used virus derived from the molecular clone SFV4. SFV4 virus does not have the same phenotype as the closely related L10 or the prototype virus from which its molecular clone was derived. In mice, L10 generates a high-titer plasma viremia, is efficiently neuroinvasive, and produces a fatal panencephalitis, whereas low-dose SFV4 produces a low-titer viremia, rarely enters the brain, and generally is avirulent. To determine the genetic differences responsible, the consensus sequence of L10 was determined and compared to that of SFV4. Of the 12 nucleotide differences, six were nonsynonymous; these were engineered into a new molecular clone, termed SFV6. The derived virus, SFV6, generated a high-titer viremia and was efficiently neuroinvasive and virulent. The phenotypic difference mapped to a single amino acid residue at position 162 in the E2 envelope glycoprotein (lysine in SFV4, glutamic acid in SFV6). Analysis of the L10 virus showed it contained different plaque phenotypes which differed in virulence. A lysine at E2 247 conferred a small-plaque avirulent phenotype and glutamic acid a large-plaque virulent phenotype. Viruses with a positively charged lysine at E2 162 or 247 were more reliant on glycosaminoglycans (GAGs) to enter cells and were selected for by passage in BHK-21 cells. Interestingly, viruses with the greatest reliance on binding to GAGs replicated to higher titers in the brain and more efficiently crossed an in vitro blood-brain barrier (BBB).IMPORTANCE Virus encephalitis is a major disease, and alphaviruses, as highlighted by the recent epidemic of chikungunya virus (CHIKV), are medically important pathogens. In addition, alphaviruses provide well-studied experimental systems with extensive literature, many tools, and easy genetic modification. In this study, we elucidate the genetic basis for the difference in phenotype between SFV4 and the virus stocks from which it was derived and correct this by engineering a new molecular clone. We then use this clone in one comprehensive study to demonstrate that positively charged amino acid residues on the surface of the E2 glycoprotein, mediated by binding to GAGs, determine selective advantage and plaque size in BHK-21 cells, level of viremia in mice, ability to cross an artificial BBB, efficiency of replication in the brain, and virulence. Together with studies on Sindbis virus (SINV), this study provides an important advance in understanding alphavirus, and probably other virus, encephalitis.

Dengue Virus Infection with Highly Neutralizing Levels of Cross-Reactive Antibodies Causes Acute Lethal Small Intestinal Pathology without a High Level of Viremia in Mice.

Severe dengue virus (DENV)-associated diseases can occur in patients who have preexisting DENV antibodies (Abs) through antibody-dependent enhancement (ADE) of infection. It is well established that during ADE, DENV-antibody immune complexes (ICs) infect Fcγ receptor-bearing cells and increase the systemic viral burden that can be measured in the blood. For protection against infection with DENV serotypes 1 to 4, strongly neutralizing Abs must be elicited to overcome the effect of ADE. Clinical observations in infants who have maternal DENV Abs or recent phase II/III clinical trials with a leading tetravalent dengue vaccine suggested a lack of correlation between Ab neutralization and in vivo disease prevention. In addressing this gap in knowledge, we found that inoculation of ICs formed with serotype cross-reactive Abs that are more than 98% neutralized in vitro promotes high mortality in AG129 mice even though peak viremia was lower than that in direct virus infection. This suggests that the serum viremia level is not always correlated with disease severity. We further demonstrated that infection with the ICs resulted in increased vascular permeability, specifically in the small intestine, accompanied with increased tissue viral load and cytokine production, which can be suppressed by anti-tumor necrosis factor alpha (anti-TNF-α) Abs. Flow cytometric analysis identified increased infection in CD11b(int) CD11c(int/hi) CD103(-) antigen-presenting cells by IC inoculation, suggesting that these infected cells may be responsible for the increase in TNF-α production and vascular permeability in the small intestine that lead to mortality in mice. Our findings may have important implications for the development of dengue therapeutics. We examined the relationship between the neutralizing level of Abs at the time of infection and subsequent disease progression in a mouse model in order to understand why patients who are shown to have a neutralizing quantity of Abs still allow sufficient DENV replication to induce severe dengue manifestations, which sometimes do not correlate with viremia level. Strikingly, we found that high mortality was induced in AG129 mice by the increase in TNF-α-induced vascular permeability accompanied by an increased viral load, specifically in the small intestine, even when the initial infection level is suppressed to less than 5% and the peak viremia level is not enhanced. This suggests that ADE overcomes the protective efficacy of Abs in a tissue-dependent manner that leads to severe small intestinal pathology. Our findings may serve to address the pathogenic role of Abs on severe dengue disease and also help to develop safe Ab-based therapeutic strategies.

Evolution of recombinant lymphocytic choriomeningitis virus/Lassa virus in vivo highlights the importance of the GPC cytosolic tail in viral fitness.

A key characteristic of arenaviruses is their ability to establish persistent infection in their natural host. Different factors like host age, viral dose strain, and route of infection may contribute to the establishment of persistence. However, the molecular mechanisms governing persistence are not fully understood. Here, we describe gain-of-function mutations of lymphocytic choriomeningitis virus (LCMV) expressing Lassa virus (LASV) GP, which can prolong viremia in mice depending on the sequences in the GP-2 cytoplasmic tail. The initial mutant variant (rLCMV/LASV mut GP) carried a point mutation in the cytosolic tail of the LASV glycoprotein GP corresponding to a K461G substitution. Unlike what occurred with the original rLCMV/LASV wild-type (wt) GP, infection of C57BL/6 mice with the mutated recombinant virus led to a detectable viremia of 2 weeks' duration. Further replacement of the entire sequence of the cytosolic tail from LASV to LCMV GP resulted in increased viral titers and delayed clearance of the viruses. Biosynthesis and cell surface localization of LASV wt and mut GPs were comparable. Starting from an emerging virus in a wild-type mouse, we engineered a panel of chimeric Lassa/lymphocytic choriomeningitis viruses. Mutants carrying a viral envelope with the cytosolic tail from the closely related mouse-adapted LCMV were able to achieve a productive viral infection lasting up to 27 days in wild-type mice. Biochemical assays showed a comparable biosynthesis and cell surface localization of LASV wt and mut GPs. These recombinant chimeric viruses could allow the study of immune responses and antivirals targeting the LASV GP.

Efficacious proteasome/HDAC inhibitor combination therapy for primary effusion lymphoma

Primary effusion lymphoma (PEL) is a rare form of aggressive B cell lymphoma caused by Kaposi's sarcoma-associated herpesvirus (KSHV). Current chemotherapy approaches result in dismal outcomes, and there is an urgent need for new PEL therapies. Previously, we established, in a direct xenograft model of PEL-bearing immune-compromised mice, that treatment with the proteasome inhibitor, bortezomib (Btz), increased survival relative to that after treatment with doxorubicin. Herein, we demonstrate that the combination of Btz with the histone deacetylase (HDAC) inhibitor suberoylanilidehydroxamic acid (SAHA, also known as vorinostat) potently reactivates KSHV lytic replication and induces PEL cell death, resulting in significantly prolonged survival of PEL-bearing mice. Importantly, Btz blocked KSHV late lytic gene expression, terminally inhibiting the full lytic cascade and production of infectious virus in vivo. Btz treatment led to caspase activation and induced DNA damage, as evidenced by the accumulation of phosphorylated γH2AX and p53. The addition of SAHA to Btz treatment was synergistic, as SAHA induced early acetylation of p53 and reduced interaction with its negative regulator MDM2, augmenting the effects of Btz. The eradication of KSHV-infected PEL cells without increased viremia in mice provides a strong rationale for using the proteasome/HDAC inhibitor combination therapy in PEL.

Transmission Potential of Two Chimeric Western Equine Encephalitis Vaccine Candidates in Culex tarsalis

Western equine encephalitis virus (WEEV) is a zoonotic alphavirus that circulates in western North America between passerine birds and mosquitoes, primarily Culex tarsalis. Since it was isolated in 1930, WEEV has caused tens of thousands of equine deaths in addition to thousands of human cases. In addition because WEEV is a virus of agricultural importance in addition to a public health threat, we developed two live-attenuated chimeric vaccine candidates that have been shown to be immunogenic and efficacious in mouse models. Vaccine candidate strains were developed by inserting the structural protein genes of WEEV strain McMillan (McM) or CO92-1356 into a Sindbis virus (SINV) strain AR339 backbone. The SIN/McM chimera also derived the N-terminal half of its capsid gene from a North American eastern equine encephalitis virus (EEEV) strain FL39-939 (henceforth referred to as SIN/EEE/McM). Although these vaccines do not generate viremia in mice, we further assessed their safety by exposing Cx. tarsalis to artificial blood meals containing high viral titers of each vaccine candidate. Both viruses exhibited a decreased rate of infection, dissemination, and transmission potential compared with the parental alphaviruses. Specifically, SIN/CO92 infected 37% of mosquitoes and disseminated in 8%, but failed to reach the saliva of the mosquitoes. In contrast, the SIN/EEE/McM virus was unable to infect, disseminate, or be transmitted in the saliva of any mosquitoes. These findings suggest that both vaccine candidates are less competent than the parental strains to be transmitted by the primary mosquito vector, Cx. tarsalis, and are unlikely to be reintroduced into a natural WEEV transmission cycle.

Differential Anti-Golgi Complex Autoantibody Production Following Murine Lactate Dehydrogenase-Elevating Virus Infection

Lactate dehydrogenase-elevating virus (LDV) causes asymptomatic infection and persistent viremia in mice with unique infectious specificity directed to a certain subpopulation of macrophages leading to chronic infection and an immunological disorder that includes hyperimmunoglobulinemia and production of autoantibodies. Infection with a species of LDV originally isolated from mice carrying an LDV-contaminated transplantable tumor (LDV-W) was reported to induce anti-Golgi complex antibody (AGA) production. In contrast, infection with the most common LDV species (LDV-P) was not associated with AGA production. Here we performed the first independent side by side comparison of the effects of the two LDV strains on their hosts as an initial approach to investigating the production of AGA. After viral inoculation, both LDV-W and LDV-P infected mice exhibited similar changes in lactate dehydrogenase in plasma suggesting similar viral activity. However, AGA production was observed in only the LDV-W infected mice and these mice exhibited plasma IgG elevation and immune complex formation. These data validated the differential potential of LDV-W and LDV-P in the production of AGA. Future comparative characterizations in the immune processing of Golgi complex autoantigens using these viral strains may be useful in obtaining specific insights in the specific anti-Golgi complex autoimmune responses.

Liver injury and viremia in mice infected with dengue-2 virus

The goal of this study was to test the feasibility of BALB/c mice as an experimental model in the study of dengue disease. BALB/c mice were intraperitoneal infected with DENV-2 obtained from a human patient. Histopathological analysis of infected animals revealed liver injury with viral antigens detection. In initial stages, the most prominent lesions were vacuolization and diffuse steatosis in hepatocytes. Serum levels of ALT and AST increased progressively, reaching the highest values 7 days p.i. and decreasing at the 14th day. Since levels of circulating virus were very low, viremia was analyzed in C6/36 cells. Virus presence was detected by ultrastructural analysis, confirmed by RT-PCR assays. Period of viremia was analyzed by flow cytometry with cells incubated with mouse-infected sera collected in different days, revealing peak virus levels at the 7th day p.i. All such data correlate to the development of the disease described in humans.

Postinfection therapy of arbovirus infections in mice

Most antiviral agents are efficacious prophylactically in vivo, and a few are efficacious for postinfection (p.i.) therapy. To explore possibilities for p.i. therapy of encephalogenic Banzi virus (BZV) and Semliki Forest virus infections in mice, we evaluated candidate antiviral therapies after development of the first clinical signs of infection. The earliest clinical indication of BZV viremia in mice is a rise in core body temperature beginning on day 3 p.i. BZV-infected mice showing elevated core body temperatures (greater than or equal to 37.3 degrees C) on days 3 and 4 p.i. were treated intraperitoneally with the interferon inducer poly(ICLC) (80 micrograms per mouse) and/or specific antiserum. Combined therapy on day 3 of a BZV infection protected over 75% of mice showing clinical evidence of viral disease before treatment. Protection against early brain infection must occur on day 4 p.i., since by that day BZV has started multiplying in the brains of the mice. Significant protection occurred with antiserum alone and increased with poly(ICLC). Similar protection was obtained during Semliki Forest virus viremia, but this infection is so rapid that the first clinical signs are reliably detectable only after viremia.

Antiviral Effects of Double‐Stranded RNA from Rice Dwarf Virus on Infection of Mice with Western Equine Encephalitis Virus

A single administration (1 to 10 mg/kg) of rice dwarf virus RNA (RDV-RNA) prior to virus challenge reduced the mortality of mice infected with western equine encephalitis (WEE) virus. The protective effect of RDV-RNA was significantly higher than that of polyinosinic-polycytidylic acid. However, when these RNAs were given after virus infection, the protective effect was negligible. The titer of circulating interferon in mice reached a peak about 5 hr after injection of these RNAs and remained at this level for about 24 hr. Viremia in mice infected with a lethal dose of WEE virus was markedly suppressed by the treatment of mice with these RNAs. A pathological examination of mice treated with a lethal dose of RDV-RNA revealed marked changes including degeneration and karyorrhexis in the lymphoid tissues of the spleen.

Effect of an immunosuppressive agent, cyclophosphamide, on chronic lactic dehydrogenase virus viremia of mice.

The immunosuppressive drug cyclophosphamide was used to study the effect of immunosuppression on the degree of chronic lactic dehydrogenase virus (LDV) viremia in mice. Weekly injections of cyclophosphamide caused an increase of LDV viremia of ca. 2.5 log(10) 50% infectious doses per ml as compared to the viremia in the nontreated mice. This increase occurred at about the same time that the formation of antibody with a neutralization index of 2 to 3 log(10) per ml could be demonstrated in the serum of control mice, whereas both neutralizing antibody and sensitized (antibody-bound but infectious) virus were absent in the immunosuppressed mice. In one experiment, antibody did not reappear 28 weeks after a 24-week course of cyclophosphamide treatment. In another experiment in which the drug was given for 12 weeks, antibody appeared again in the treated mice 14 weeks after cessation of drug administration and was accompanied by a decrease in viremia. The normal decrease of early viremia during the first 2 weeks of infection in immunosuppressed mice suggests that the immune response is not the cause of this initial decrease in LDV viremia but that interferon and perhaps other nonimmune factors may be involved here. The increased viremia in the immunosuppressed mice during the later stages of infection indicates that the immune response plays an important role in partial control of chronic viremia. The quantitative correlation between the decrease in neutralizing antibody and the increase in viremia in immunosuppressed mice suggests that antibody rather than cellular immunity may be the more important immune factor in the control of chronic viremia.

Enhanced Severity of Experimental Herpes simplex Infection in Mice Fed a Protein-free Diet

Four-week old weanling ICR male mice were made hypoproteinemic after feeding them an experimental protein-free diet for one week. Their capacity to respond to infection with Herpes simplex virus was compared with that of a group of mice fed a regular diet and whose serum protein content was normal. Mice fed the protein-free diet differed from the normal group in the following respects: 1) They had higher mortality, since a dose sufficient to kill all mice fed a protein-free diet in 9 days killed only 20% of the normal mice. 2) Although both groups developed viremia, the mice fed the protein-free diet had a 100-fold greater blood concentration of the virus; moreover, viremia persisted until death in the deficient mice, whereas it terminated in the normal ones between 36 and 42 hours. 3) The minimal dose sufficient to induce viremia in the mice fed the protein-free diet was tenfold lower than the one required to induce viremia in the normoproteinemic mice. 4) Mice fed the protein-free diet consistently developed encephalitis, whereas in normoproteinemic mice, encephalitis occurred only sporadically. Since both groups developed an interferon-like inhibitor in comparable quantities and neither group produced antibodies against H. simplex during the time these differences between the 2 groups were observed, failure of other defense mechanisms in the mice fed the protein-free diet must be responsible for the enhanced severity of H. simplex infection in them.

Alteration of the course of lymphocytic choriomeningitis in mice by certain antimetabolites

Azaserine, 6-diazo-5-oxo-nor-1-leucine (DON), and 5-fluorouracil were shown to prolong the lives of mice injected intracerebrally with the virus of lymphocytic choriomeningitis, but less effectively than amethopterin. Azaserine and DON prolonged duration of demonstrable viremia in mice given the virus subcutaneously (5-fluorouracil was not tested). The sparing effect of amethopterin was partly overcome by injecting a mixture of purines and pyrimidines, as free bases, nucleosides, and nucleotides. It is suggested that amethopterin may act in another way in addition to its interference with nucleic acid biosynthesis.

Viremia in mice with pulmonary influenza A virus infections.

Abstract Viremia occurs in mice infected intranasally or in the cloud chamber with lethal doses of influenza A (PR8 virus). The incidence of viremia in mice killed at forty-eight hours after infection varied from 20 to 50 per cent in mice allowed to breathe highly lethal clouds of nebulized virus. With few exceptions viremia occurred only in animals after the concentration of influenza virus in the lungs had reached a high level. On the other hand, virus was not isolated from the blood of many animals with similar lung titers so that the incidence of viremia could not be correlated with the amount of virus or the pathologic findings in the lungs. Viremia in experimental pulmonary infections in mice is probably sporadic with the amount of virus in the blood at any one time being small and close to the minimal infecting dose in fertile eggs when inoculated intra-allantoically. The duration of viremia in individual mice could not be determined accurately because of the small amount of blood available for virus analysis. When influenza virus enters the blood from the lungs it quickly becomes attached to the red blood cells. Whether the virus-coated cells become agglutinated in vivo was not determined. Following the intravenous injection of influenza virus it rapidly disappears from the blood but can be detected for significantly longer periods in the spleen, liver, and lung. The possible significance of viremia in relation to the pathogenesis and immune response in experimental infections in mice is discussed.