Interferon-γ Inhibits Ebola Virus Infection

Interferon-γ Inhibits Ebola Virus Infection For years I’ve been telling students to forget about type II (gamma) interferon in terms of protecting against viruses – antiviral therapy is mostly down to type I (alpha/beta) interferon. Well not in the case of Ebola virus seemingly.

With no current approved filovirus therapeutics, the recent Ebola virus epidemic in Guinea, Sierra Leone and Liberia emphasizes the need for effective treatments against this highly pathogenic family of viruses. The use of this drug to inhibit Ebola virus infection would allow rapid implementation of a novel antiviral therapy for future crises. Interferon gamma elicits an antiviral state in antigen-presenting cells and stimulates cellular immune responses. This paper demonstrates that interferon gamma profoundly inhibits Ebola virus infection of macrophages, which are early cellular targets of Ebola virus and identifies novel interferon gamma-stimulated genes in human macrophage populations that have not been previously appreciated to inhibit filoviruses or other negative strand RNA viruses. It also shows that interferon gamma given 24 hours prior to or after virus infection protects mice from lethal Ebola virus challenge, suggesting that this drug may serve as an effective prophylactic and/or therapeutic strategy against this deadly virus.


Interferon-γ Inhibits Ebola Virus Infection. (2015) PLoS Pathog 11(11): e1005263. doi:10.1371/journal.ppat.1005263
Ebola virus outbreaks, such as the 2014 Makona epidemic in West Africa, are episodic and deadly. Filovirus antivirals are currently not clinically available. Our findings suggest interferon gamma, an FDA-approved drug, may serve as a novel and effective prophylactic or treatment option. Using mouse-adapted Ebola virus, we found that murine interferon gamma administered 24 hours before or after infection robustly protects lethally-challenged mice and reduces morbidity and serum viral titers. Furthermore, we demonstrated that interferon gamma profoundly inhibits Ebola virus infection of macrophages, an early cellular target of infection. As early as six hours following in vitro infection, Ebola virus RNA levels in interferon gamma-treated macrophages were lower than in infected, untreated cells. Addition of the protein synthesis inhibitor, cycloheximide, to interferon gamma-treated macrophages did not further reduce viral RNA levels, suggesting that interferon gamma blocks life cycle events that require protein synthesis such as virus replication. Microarray studies with interferon gamma-treated human macrophages identified more than 160 interferon-stimulated genes. Ectopic expression of a select group of these genes inhibited Ebola virus infection. These studies provide new potential avenues for antiviral targeting as these genes that have not previously appreciated to inhibit negative strand RNA viruses and specifically Ebola virus infection. As treatment of interferon gamma robustly protects mice from lethal Ebola virus infection, we propose that interferon gamma should be further evaluated for its efficacy as a prophylactic and/or therapeutic strategy against filoviruses. Use of this FDA-approved drug could rapidly be deployed during future outbreaks.

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History and origin of the HIV-1 epidemic in South Africa

History and origin of the HIV-1 epidemic in South Africa HIV has spread at an alarming rate in South Africa, making it the country with the highest number of HIV infections. Several studies have investigated the histories of HIV-1 subtype C epidemics but none have done so in the context of social and political transformation in southern Africa. There is a need to understand how these processes affects epidemics, as socio-political transformation is a common and on-going process in Africa. A new paper genotypes HIV strains from the start of the epidemic and determines the history of the southern Africa and South African epidemic.

The southern African epidemic’s estimated dates of origin was placed around 1960, while dynamic reconstruction revealed strong growth during the 1970s and 80s. The South African epidemic has a similar origin, caused by multiple introductions from neighbouring countries, and grew exponentially during the 1980s and 90s, coinciding with socio-political changes in South Africa. These findings provide an indication as to when the epidemic started and how it has grown, while the inclusion of sequence data from the start of the epidemic provided better estimates. The epidemic have stabilized in recent years with the expansion of antiretroviral therapy.

History and origin of the HIV-1 subtype C epidemic in South Africa and the greater southern African region. (2015) Sci. Rep. 5, 16897; doi: 10.1038/srep16897

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Exploring vulnerabilities of Cryptosporidium

Cryptosporidium parvum Cryptosporidium parvum is a gastrointestinal parasite that can cause moderate to severe diarrhoea in children and adults, and deadly opportunistic infection in AIDS patients. Because C. parvum is resistant to chlorine disinfectant treatment, it frequently causes water-borne outbreaks around the world. A new study looks at a C. parvum protein that is central to glycolysis – the only pathway by which the parasite can generate energy – and identifies it as a potential drug target.

Researchers studied the parasite’s metabolism during its complicated life-cycle. C. parvum exists both in free stages (where parasites are in the environment or in the host’s digestive tract) and intracellular stages following host cell invasion, during which the parasite occupies a specialized compartment – the parasitophorous vacuole – which is delineated by a host-cell derived border called the parasitophorous vacuole membrane. Glycolysis is the only metabolic process by which organisms like C. parvum that lack functional mitochondria to derive energy from oxygen can generate ATP, the universal biological energy storage molecule. They found that the C. parvum LDH (CpLDH) protein is found inside the parasite’s cells during the free stages, but is then transferred to the PVM during intracellular development, indicating involvement of the parasitophorous vacuole membrane in parasite energy metabolism, and specifically, in lactate fermentation. They also showed that two known LDH inhibitors can inhibit both CpLDH activity and parasite growth.

These observations not only reveal a new function for the poorly understood PVM structure in hosting the intracellular development of C. parvum, but also suggest LDH as a potential target for developing therapeutics against this opportunistic pathogen, for which fully effective treatments are not yet available.


Cryptosporidium Lactate Dehydrogenase Is Associated with the Parasitophorous Vacuole Membrane and Is a Potential Target for Developing Therapeutics. PLoS Pathog 11(11): e1005250. doi: 10.1371/journal.ppat.1005250
The apicomplexan, Cryptosporidium parvum, possesses a bacterial-type lactate dehydro- genase (CpLDH). This is considered to be an essential enzyme, as this parasite lacks the Krebs cycle and cytochrome-based respiration, and mainly–if not solely, relies on glycolysis to produce ATP. Here, we provide evidence that in extracellular parasites (e.g., sporozoites and merozoites), CpLDH is localized in the cytosol. However, it becomes associated with the parasitophorous vacuole membrane (PVM) during the intracellular developmental stages, suggesting involvement of the PVM in parasite energy metabolism. We characterized the biochemical features of CpLDH and observed that, at lower micromolar levels, the LDH inhibitors gossypol and FX11 could inhibit both CpLDH activity. These observations not only reveal a new function for the poorly understood PVM structure in hosting the intracellular development of C. parvum, but also suggest LDH as a potential target for developing therapeutics against this opportunistic pathogen, for which fully effective treatments are not yet available.

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Targeting the host rather than the virus

Chronic hepatitis C virus (HCV) infection is a major cause of liver cirrhosis and hepatocellular carcinoma (HCC) which are leading indications of liver transplantation. To date, there is no vaccine to prevent HCV infection and liver transplantation is invariably followed by infection of the liver graft.

Hepatitis C virus replication cycle

In the past years, direct-acting antivirals (DAAs) have had a major impact on the management of chronic hepatitis C, which has become a curable disease in the majority of DAA-treated patients. In contrast to DAAs that target viral proteins, host-targeting agents (HTAs) interfere with cellular factors involved in the viral life cycle. By acting through a complementary mechanism of action and by exhibiting a generally higher barrier to resistance, HTAs offer a prospective option to prevent and treat viral resistance. Given their complementary mechanism of action, HTAs and DAAs can act in a synergistic manner to reduce viral loads.

This review summarizes the different classes of HTAs against HCV infection that are in preclinical or clinical development and highlights their potential to prevent HCV infection, e.g., following liver transplantation, and to tailor combination treatments to cure chronic HCV infection.

Host-Targeting Agents to Prevent and Cure Hepatitis C Virus Infection. Viruses 2015, 7(11), 5659-5685; doi: 10.3390/v7112898

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Towards a safe and efficient SARS-coronavirus vaccine

Lung tissue infected with SARS-CoV Zoonotic coronaviruses, including SARS-CoV and Middle East respiratory syndrome (MERS-CoV), have recently emerged causing high morbidity and mortality in human or piglets. No fully protective therapy is still available for these CoVs and the development of efficient vaccines is a high priority.

Live attenuated vaccines are considered most effective compared to other types of vaccines, as they induce a long-lived, balanced immune response. However, safety is the main concern of this type of vaccines because attenuated viruses can eventually revert to a virulent phenotype. Therefore, an essential feature of any live attenuated vaccine candidate is its stability. In addition, introduction of several safety guards is advisable to increase vaccine safety.

This paper analyzes the mechanisms by which an attenuated SARS-CoV reverted to a virulent phenotype and describes the introduction of attenuating deletions that maintained virus stability. The virus, engineered with two safety guards, provided full protection against challenge with a lethal SARS-CoV. Both humoral and cellular responses are relevant to protect from SARS. The viruses generated in this work express all virus proteins, except for small regions deleted in the E and nsp1 proteins, and therefore have the potential of inducing both antibody and T cell responses, making this type of live vaccine more attractive than subunit or non replicating virus vaccines. Understanding of the molecular mechanisms by which an attenuated SARS-CoV reverted to a virulent phenotype could also be applied to the development of other relevant CoVs vaccines, such as MERS-CoV.

Identification of the Mechanisms Causing Reversion to Virulence in an Attenuated SARS-CoV for the Design of a Genetically Stable Vaccine. (2015) PLoS Pathog 11 (10): e1005215. doi:10.1371/journal.ppat.1005215
A SARS-CoV lacking the full-length E gene (SARS-CoV-∆E) was attenuated and an effective vaccine. Here, we show that this mutant virus regained fitness after serial passages in cell culture or in vivo, resulting in the partial duplication of the membrane gene or in the insertion of a new sequence in gene 8a, respectively. The chimeric proteins generated in cell culture increased virus fitness in vitro but remained attenuated in mice. In contrast, during SARS-CoV-∆E passage in mice, the virus incorporated a mutated variant of 8a protein, resulting in reversion to a virulent phenotype. When the full-length E protein was deleted or its PDZ-binding motif (PBM) was mutated, the revertant viruses either incorporated a novel chimeric protein with a PBM or restored the sequence of the PBM on the E protein, respectively. Similarly, after passage in mice, SARS-CoV-∆E protein 8a mutated, to now encode a PBM, and also regained virulence. These data indicated that the virus requires a PBM on a transmembrane protein to compensate for removal of this motif from the E protein. To increase the genetic stability of the vaccine candidate, we introduced small attenuating deletions in E gene that did not affect the endogenous PBM, preventing the incorporation of novel chimeric proteins in the virus genome. In addition, to increase vaccine biosafety, we introduced additional attenuating mutations into the nsp1 protein. Deletions in the carboxy-terminal region of nsp1 protein led to higher host interferon responses and virus attenuation. Recombinant viruses including attenuating mutations in E and nsp1 genes maintained their attenuation after passage in vitro and in vivo. Further, these viruses fully protected mice against challenge with the lethal parental virus, and are therefore safe and stable vaccine candidates for protection against SARS-CoV.

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Interrupting the transmission cycle of dengue virus

Dengue virus-infected cells Dengue virus is responsible for serious human disease worldwide. The World Health Organization estimates that over 2 billion people are at risk for this disease. There are currently no vaccines or specific antiviral medications currently available for dengue virus infection. The virus is transmitted to humans by infected mosquitoes during feeding and probing. By examining the effects of virus infection on gene expression, and interactions between virus and vector, it may be able to find new targets for prevention and treatment.

A new paper looks at a mosquito protein, CRVP379, whose expression was highly increased during dengue virus infection in mosquitoes. There is a requirement for CRVP379 during dengue virus infection in the mosquito and a correlation between the levels of CRVP379 and levels of infection. The results indicate that the protein may be acting with a putative dengue virus receptor in the mosquito, prohibitin protein. These data also suggest that blocking CRVP379 function may be used to block dengue virus infection in the mosquito.

Dengue Virus Infection of Aedes aegypti Requires a Putative Cysteine Rich Venom Protein. (2015) PLoS Pathog 11(10): e1005202. doi: 10.1371/journal.ppat.1005202
Dengue virus (DENV) is a mosquito-borne flavivirus that causes serious human disease and mortality worldwide. There is no specific antiviral therapy or vaccine for DENV infection. Alterations in gene expression during DENV infection of the mosquito and the impact of these changes on virus infection are important events to investigate in hopes of creating new treatments and vaccines. We previously identified 203 genes that were 5-fold differentially upregulated during flavivirus infection of the mosquito. Here, we examined the impact of silencing 100 of the most highly upregulated gene targets on DENV infection in its mosquito vector. We identified 20 genes that reduced DENV infection by at least 60% when silenced. We focused on one gene, a putative cysteine rich venom protein (SeqID AAEL000379; CRVP379), whose silencing significantly reduced DENV infection in Aedes aegypti cells. Here, we examine the requirement for CRVP379 during DENV infection of the mosquito and investigate the mechanisms surrounding this phenomenon. We also show that blocking CRVP379 protein with either RNAi or specific antisera inhibits DENV infection in Aedes aegypti. This work identifies a novel mosquito gene target for controlling DENV infection in mosquitoes that may also be used to develop broad preventative and therapeutic measures for multiple flaviviruses.

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Cell-to-cell infection by HIV contributes over half of virus infection

Cell-to-cell infection by HIV Viruses such as HIV-1 replicate by invading and hijacking cells, forcing the cells to make new copies of the virus. These copies then leave the cell and continue the infection by invading and hijacking new cells. There are two ways that viruses may move between cells, which are known as ‘cell-free’ and ‘cell-to-cell’ infection. In cell-free infection, the virus is released into the fluid that surrounds cells and moves from there into the next cell. In cell-to-cell infection the virus instead moves directly between cells across regions where the two cells make contact.

Previous research has suggested that cell-to-cell infection is important for the spread of HIV-1. However, it is not known how much the virus relies on this process, as it is technically challenging to perform experiments that prevent cell-free infection without also stopping cell-to-cell infection. Researchers have overcome this problem by combining experiments on laboratory-grown cells with a mathematical model that describes how the different infection methods affect the spread of HIV-1. This revealed that the viruses spread using cell-to-cell infection about 60% of the time, which agrees with results previously found by another group of researchers. They also found that cell-to-cell infection increases how quickly viruses can infect new cells and replicate inside them, and improves the fitness of the viruses.

The environment around cells in humans and other animals is different to that found around laboratory-grown cells, and so more research will be needed to check whether this difference affects which method of infection the virus uses. If the virus does spread in a similar way in the body, then blocking the cell-free method of infection would not greatly affect how well HIV-1 is able to infect new cells. It may instead be more effective to develop HIV treatments that prevent cell-to-cell infection by the virus.

Cell-to-cell infection by HIV contributes over half of virus infection. (2015) eLife 4: e08150 doi: 10.7554/eLife.08150
Cell-to-cell viral infection, in which viruses spread through contact of infected cell with surrounding uninfected cells, has been considered as a critical mode of virus infection. However, since it is technically difficult to experimentally discriminate the two modes of viral infection, namely cell-free infection and cell-to-cell infection, the quantitative information that underlies cell-to-cell infection has yet to be elucidated, and its impact on virus spread remains unclear. To address this fundamental question in virology, we quantitatively analyzed the dynamics of cell-to-cell and cell-free human immunodeficiency virus type 1 (HIV-1) infections through experimental-mathematical investigation. Our analyses demonstrated that the cell-to-cell infection mode accounts for approximately 60% of viral infection, and this infection mode shortens the generation time of viruses by 0.9 times and increases the viral fitness by 3.9 times. Our results suggest that even a complete block of the cell-free infection would provide only a limited impact on HIV-1 spread.

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Malaria in pregnancy alters foetal neurovascular development

Malaria in pregnancy alters foetal neurovascular development A growing body of evidence has established the importance of the in utero environment on neurodevelopment and long-term cognitive and behavioral outcomes. These data suggest factors that disrupt the tightly regulated in utero environment can modify normal neurodevelopmental processes. Approximately 125 million pregnancies worldwide are at risk of malaria infection every year. However the impact of in utero exposure to malaria in pregnancy on fetal neurodevelopment is unknown.

Researchers used a mouse model of malaria in pregnancy to examine the impact of maternal malaria exposure on neurocognitive outcomes in offspring. They observed impaired learning and memory and depressive-like behavior in malaria-exposed offspring that were neither congenitally infected nor low birth weight. These neurocognitive impairments were associated with decreased tissue levels of neurotransmitters in regions of the brain linked to the observed deficits. Disruption of maternal C5a complement receptor signaling restored the levels of neurotransmitters and rescued the associated cognitive phenotype observed in malaria-exposed offspring. This study provides the first evidence implicating a causal link between pre-natal exposure to malaria, complement signaling and subsequent neurocognitive impairment in offspring.

Experimental Malaria in Pregnancy Induces Neurocognitive Injury in Uninfected Offspring via a C5a-C5a Receptor Dependent Pathway. (2015) PLoS Pathog 11 (9): e1005140. doi:10.1371/journal.ppat.1005140
The in utero environment profoundly impacts childhood neurodevelopment and behaviour. A substantial proportion of pregnancies in Africa are at risk of malaria in pregnancy (MIP) however the impact of in utero exposure to MIP on fetal neurodevelopment is unknown. Complement activation, in particular C5a, may contribute to neuropathology and adverse outcomes during MIP. We used an experimental model of MIP and standardized neurocognitive testing, MRI, micro-CT and HPLC analysis of neurotransmitter levels, to test the hypothesis that in utero exposure to malaria alters neurodevelopment through a C5a-C5aR dependent pathway. We show that malaria-exposed offspring have persistent neurocognitive deficits in memory and affective-like behaviour compared to unexposed controls. These deficits were associated with reduced regional brain levels of major biogenic amines and BDNF that were rescued by disruption of C5a-C5aR signaling using genetic and functional approaches. Our results demonstrate that experimental MIP induces neurocognitive deficits in offspring and suggest novel targets for intervention.

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Adipose Tissue Is a Neglected HIV Reservoir

Skin Chronic immune activation/inflammation and viral persistence in reservoirs are important features of chronic HIV infection, even in patients receiving ART. A recent paper evaluates the involvement of adipose tissue in chronic HIV/SIV infections.

Adipose tissue accounts for 15 to 20% of the body weight, contains both adipocytes and (within the stromal vascular fraction) immune cells, and exerts crucial metabolic and immune activities. It might provide an ideal environment for HIV persistence and immune inflammation.

The authors showed that viraemic SIV-infected macaques had elevated levels of immune activation and inflammation in adipose tissue, and that both resident CD4+ T cells and macrophages were infected. In similar experiments in ART-controlled HIV-infected patients, HIV DNA was detected in the stromal vascular fraction of adipose tissue (more specifically, in adipose tissue CD4+ T cells). Replication-competent HIV was detected in ex vivo- activated, sorted adipose tissue CD4+ T cells from six aviremic, ART-treated patients. Thus, adipose tissue may constitute a viral reservoir and be involved in long-term immune activation and inflammation—even in ART-suppressed patients. Given that adipose tissue is strongly regulated by both metabolic and immune pathways, modulating adipose tissue may constitute a valuable means of limiting both viral persistence and chronic inflammation in HIV-infected patients even ART-controlled.

Adipose Tissue Is a Neglected Viral Reservoir and an Inflammatory Site during Chronic HIV and SIV Infection. (2015) PLoS Pathog 11 (9): e1005153. doi: 10.1371/journal.ppat.1005153
Two of the crucial aspects of human immunodeficiency virus (HIV) infection are (i) viral persistence in reservoirs (precluding viral eradication) and (ii) chronic inflammation (directly associated with all-cause morbidities in antiretroviral therapy (ART)-controlled HIV-infected patients). The objective of the present study was to assess the potential involvement of adipose tissue in these two aspects. Adipose tissue is composed of adipocytes and the stromal vascular fraction (SVF); the latter comprises immune cells such as CD4+ T cells and macrophages (both of which are important target cells for HIV). The inflammatory potential of adipose tissue has been extensively described in the context of obesity. During HIV infection, the inflammatory profile of adipose tissue has been revealed by the occurrence of lipodystrophies (primarily related to ART). Data on the impact of HIV on the SVF (especially in individuals not receiving ART) are scarce. We first analyzed the impact of simian immunodeficiency virus (SIV) infection on abdominal subcutaneous and visceral adipose tissues in SIVmac251 infected macaques and found that both adipocytes and adipose tissue immune cells were affected. The adipocyte density was elevated, and adipose tissue immune cells presented enhanced immune activation and/or inflammatory profiles. We detected cell-associated SIV DNA and RNA in the SVF and in sorted CD4+ T cells and macrophages from adipose tissue. We demonstrated that SVF cells (including CD4+ T cells) are infected in ART-controlled HIV-infected patients. Importantly, the production of HIV RNA was detected by in situ hybridization, and after the in vitro reactivation of sorted CD4+ T cells from adipose tissue. We thus identified adipose tissue as a crucial cofactor in both viral persistence and chronic immune activation/inflammation during HIV infection. These observations open up new therapeutic strategies for limiting the size of the viral reservoir and decreasing low-grade chronic inflammation via the modulation of adipose tissue-related pathways.

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