Category Archives: Guest Blogger

Guest Blogger, Immunology, Pathogenesis

Mouse Pneumonia: Are We to Blame?

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Contributed by guest blogger: Alix Zongrone ’12

Pneumonia virus of mice, or PVM, is the leading cause of pneumonia in laboratory mice; however, lack of evidence of PVM in wild rodents has left scientists in the dark with regards to the history and natural host of the virus. Because PVM is mostly found in captive settings (i.e. laboratories, pet shops, etc.) and PVM-neutralizing behavior has been observed in human cells, it has been suggested that human contact may play a pivotal role in the virus’s spread. Several studies have sought to investigate the prevalence of PVM in humans and its role in human respiratory infection; however, since PVM is closely related to human respiratory syncytial virus, or RSV, it is difficult to make sound conclusions based on this evidence alone.

Due to the evidence of PVM in humans, researchers inoculated two different non-human primate species with PVM to investigate replication activity of PVM in these mammals. They found that, over the course of twelve days, most of the samples exhibited viral replication as well as viral shedding. Although not all of the animals showed virus replication and shedding behavior, PVM antibodies were found in all test animals, suggesting that infection did take place, but replication was highly restricted. Though PVM was observed to not replicate well in non-human primates, human lung epithelial cells exhibited similar permissiveness of both PVM and RSV in vitro.
Controlling the interferon (IFN) immune response is a known mechanism of successful viral replication in the host. Researchers investigated the ability of PVM to block IFN response to further explore PVM host range restriction. The virus demonstrated an ability to block IFN response in these human epithelial cells thanks to the NS2 protein. However, a Western blot was used to compare proteins made from PVM and RSV and  PVM-neutralizing activity specificity was also determined. Humans were tested for PVM antibodies to examine whether an immune response was triggered. No PVM antibodies were found in the human sera, and no reactivity between PVM proteins and observed PVM-neutralizing behavior was recorded. This demonstrates a lack of immune response in the human cells.
Although PVM was observed to replicate in vitro in human epithelial cells, the results remain inconclusive as to whether or not the virus should be considered a human pathogen. The lack of permissiveness in non-human primates suggests that the virus may not actually cause infection in humans. This is supported by the lack of reaction shown between PVM proteins and PVM-neutralizing activity in the Western Blot.
Questions remain as to the nature of the PVM-neutralizing activity in human serum as well the origin of PVM and its natural host. Is that which is categorized as PVM-neutralizing behavior not actually PVM-specific? What is causing PVM in captive laboratory mice but not in wild rodent species?  Finally, what could possibly be the natural host of pneumonia virus of mice, if not mice?

Link: http://jvi.asm.org/content/86/10/5829.abstract?etoc

Alix Zongrone is a senior at Vassar College, majoring in biology.

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Guest Blogger, Immunology, Vaccines

After many setbacks, cross-presentation provides new hope for a Herpes Simplex Virus 1 vaccine

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Contributed by guest blogger: Stephanie Mischell ’12

Herpes simplex virus type 1 (HSV-1) is making news due to a paper by Jing et al identifying two promising new candidate antigens for a vaccine. HSV-1 is a widespread public health issue, infecting approximately 60% of Americans and causing symptoms, most likely cold sores or genital sores but on rare occasion blindness or fatal brain damage. Furthermore, finding a vaccine for HSV-1 has proved difficult, in part because of the vital but elusive role of CD8+ T-cells in the HSV-1 immune response. Mice studies suggest that a CD8-response could facilitate memory cell formation and ameliorate chronic disease caused by HSV-1, but human blood does not have many HSV-1 specific CD8+ T-cells and very few CD8 epitopes have been identified.  Previous attempts at vaccines most recently using the HSV glycoprotein D (gD2), have focused on CD4+ T-cell specific epitopes. These attempts were unable to stimulate a CD8+ T-cell response, and the vaccine failed during clinical trials. A way to stimulate both CD4+ and CD8+ T-cell responses seems necessary to create an effective vaccine.

Jing et al’s work is significant because it harnesses properties originally used to study HSV-2 to identify HSV-1 epitopes recognized by CD8+ T-cells. An epitope, or antigenic determinant, is the part of an antigen that is recognized by the immune system; this interaction is what triggers a host immune response. Jing et al demonstrated previously that in vitro monocyte-derived dendritic cells (moDC’s), or antigen-presenting cells, can cross-present HSV-2  epitopes to create  HSV-2 specific memory T-cells. In this paper, they harnessed this cross-reactivity of moDC’s and applied it to HSV-1, stimulating and identifying HSV-1 specific CD8+ T-cells. 45 distinct CD8+ T-cell epitopes were identified. Furthermore, the genomes of host responder cells were cloned, and HSV-1 epitopes were analyzed for HLA restriction. Proteins from two genes, UL39 and UL46, were identified as most highly restricted, suggesting that they are most involved in the immunogenic response. PMBC assays confirmed these results quantitatively.

Jing et al conclude that the viral proteins coded by UL39 and UL46 are good candidate antigens for an HSV-1 vaccine because of their CD4+ and CD8+ T-cell  immunogenicity. However, they also acknowledge that their sample size is small and that subunit vaccines have not been successful vaccines for HSV-1. In fact, the large number of CD8+ T-cell   epitopes identified led the authors to conclude that a whole-virus vaccine may be more successful than subunits. Most of the failed vaccines showed similar promise until phase II or phase III of clinical trials, suggesting that the small amount of data from this study is just a start. This discovery is important but not a guaranteed vaccine.

While the identification of UL39 and UL46 are important steps in solving the public health issue posed by HSV-1, as is the identification of other CD8+ T-cell   epitopes, perhaps the most significant part of the study is the implications of their novel research methods on the study of viral vaccines. The enrichment techniques used could potentially make studying T-cell responses easier. The authors confirmed the applicability of their methods by using the same techniques to study the vaccinia virus, a microbe with a large genome of over 200 genes. This paper demonstrates a small advancement in HSV-1 research and control, but may have larger implications for this and other large viruses.

Link to original article: http://www.jci.org/articles/view/60556

Stephanie Mischell is a senior at Vassar College, majoring in biology.

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Guest Blogger, Immunology

The Viral Theory of Schizophrenia

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Contributed by guest blogger: Hannah Ziobrowski ’12

Schizophrenia is a severely debilitating mental illness with no known cause or cure, although there is a strong genetic correlation.  Interestingly, there is additionally a significant relationship between season of birth and the development of schizophrenia, as individuals born during late winter and spring have a significantly increased risk for developing schizophrenia.  One hypothesis to explain this phenomenon is that this is due to prenatal viral infection, which is more likely to occur in the winter months.  It is hypothesized that viral infections occurring during the third trimester of pregnancy result in the increased risk for developing schizophrenia.  However, there is currently debate as to how this happens- is it due to a direct viral infection of the fetus, or due to maternal cytokines in response to infection?

A study by Faterni et al (2012) found that the placenta may be a site of pathology in viral infections.  Using pregnant mice infected with a sublethal dose of influenza on the seventh day of pregnancy (E7), they found that viral infection resulted in many histological abnormalities in the placentae.  These abnormalities included an absence of the labyrinth zone, the region of the maternal placenta in which nutrients and oxygen are exchanged between the maternal and fetal blood, the presence of thrombi, and an increased number of inflammatory cells.  Additionally, microarray analyses revealed a significant upregulation of 77 genes and downregulaton of 93 genes in the placentae of infected mothers, compared to sham-infected mothers.  20% of these altered genes were involved in apoptotic or anti-apoptotic pathways, 10% were associated with immune response, 11% were involved with hypoxia, and about 11% were involved with inflammation.  9.4% were associated with major mental disorders including schizophrenia, bipolar disorder, major depression, and autism.  All of these changes could potentially affect developing embryos.  The deletion of a labyrinth zone could result in a reduction of oxygen delivered to the developing fetus and result in neural abnormalities, which may be ultimately caused by an inflammatory immune response.

The authors also analyzed gene expression in the hippocampus and prefrontal cortex of the offspring of infected mothers.  Compared to offspring of sham-infected mothers, they found 6 upregulated and 24 downregulated genes in the prefrontal cortex at the first day after birth (P0), and 4 upregulated and 13 downregulated genes in the hippocampus at P0.  Genes in the prefrontal cortex that showed a significant alteration in expression included glutamate receptor interacting protein I, platelet factor 4, contactin 1, and neurotrophic tyrosine kinase receptor type 3.  Important genes in the hippocampus that showed altered levels of expression included paralemmin 2, and protein tyrosine kinase 2 beta.  In total, 40 different genes showed altered expression in the two areas at P0 after infection at E7 (first trimester), compared to 39 at E9, 676 at E16, and 247 at E18 (as found in previous studies).   These altered expression levels most likely reflect altered neural organization.

Importantly, HINI viral genes were not detected in either the placenta or brains of offspring whose mothers were infected at E7, suggesting that the virus did not cross the placenta to directly infect the offspring.  This consequently implicates that the changes found in gene expression as well as the structural abnormalities of the placenta were most likely due to the production of maternal or fetal cytokines, most likely due to an increase in inflammatory cells in infected placenta.

These data overall illustrate that viral infections during pregnancy can lead to an inflammatory response and structural abnormalities in the placenta.  These structural abnormalities may cause significant alterations in oxygen and nutrients delivered to the fetus, causing abnormalities in the overall development of the fetus, including the brain.  Could these organizational neural abnormalities lead to an increased risk for developing schizophrenia later in life?

A next step for the authors would be to directly check the levels of cytokines in the placenta in order to assess the inflammatory response. Furthermore, are these results also found with infection of other viruses?  Or are they more or less significant depending on the virus and time of infection?

Link: http://www.sciencedirect.com/science/article/pii/S0028390811000141

Hannah Ziobrowski is a senior at Vassar College, majoring in Neuroscience and Behavior.

 

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Environmental virology, Guest Blogger

Herpes-Family Viruses are Associated with Stressed Out Corals

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Contributed by guest blogger: Ian Heller ‘12

A new review out in the Journal of Experimental Marine Biology and Ecology is causing a rash of media attention regarding the presence of viruses in stressed out coral. However, this media attention, with catchy titles playing at old stigmas against herpes infection in humans, misses the true story told being uncovered in the new field of coral virology. What has the science actually shown?

Coral reefs are hotspots of biodiversity and essential components of the ocean ecosystem. Corals themselves contain an amazingly diverse assembly of different organisms. Tiny organisms like symbiotic algae, fungi bacteria, and archaea are all necessary for healthy coral. Unfortunately, coral reefs are threatened world wide due to rising sea temperatures, acidifying ocean water, and pollution in the form of sewage and fertilizer runoff. These stressors seem linked to an increased incidence of disease in coral, but what pathogens are actually making corals sick?

To investigate whether any viruses were associated with stressed coral, researchers compared the metagenomes of healthy corals and corals grown in water that was too hot, too acidic, too polluted with organic carbon (to simulate sewage stress) or too polluted with plant fertilizer nutrients. Within this “metagenome” is all of the DNA sequences from all of the different algae, bacteria, virus, etc., that are part of each sample, in this case, a coral fragment.

The first step in making such a comparison is sequencing as many of the genes as possible each sample, a feat made feasible by the increasing accessibility of gene sequencing. Next, researchers identify all of the sequences in their samples’ “library” of genes that correspond to viral genes. This means sifting through over 51,000 sequences! To figure out the identify of these sequences, the researchers use a computer algorithm known as BLAST to compared their unknown sequences with known sequences in National Center for Biotechnology Information’s public database of nucleic acid sequences. Then, to find their “viral needles” in the “metagenome haystack”, they use various computational approaches to eliminate non-viral sequences and identify viral sequences. In their results, the researchers found viral sequence from 19 different virus families. Then, when the metagenomes from healthy corals were compared to stressed corals, it was found that the stressed corals had an increased frequency of herpes-virus family sequences.

To confirm that this frequency shift actually corresponded to more herpes genes in stressed corals, the researchers used Real-Time PCR (also know as quatitative PCR) to measure the concentrations of a specific nucleic acid sequence in different corals.  The nucleic acid sequence that was focused on was a herpes virus sequence similar (62% identical) to the thymidylate synthase gene from Saimiriine herpesvirus 2. This experiment showed that indeed, stressed corals tended to have more of this gene in their metagenome than their healthy counterparts.

This study provides an excellent first step into the world of coral virology; it identifies possible candidate viruses that may be contributing to coral illness. However many more questions need to be answered to understand viruses’ role in coral health. For example, few studies have actually observed virus actively hosted by a coral, and none have yet shown that herpes-like viruses can make healthy, unstressed corals sick. The ecological role of viruses may turn out to be surprisingly complex. Some researchers have even proposed that viruses may be necessary for coral survival. Corals host symbiotic algae within their cells, in a mutualism that is a requirement for corals to survive. In order to live inside coral cells, the algae must somehow evade or suppress the corals innate immune response, just as many viruses must do. Will future studies discover a link between the algae infection and virus infection?

Links:

http://dx.doi.org/10.1016/j.jembe.2011.07.030

http://www.pnas.org/content/105/47/18413.full

Ian Heller is a senior at Vassar, majoring in biology.  He is also good at making puns, and had a hard time choosing a title for this article.  Rejected titles included: Catching herpes from coral sex, Viruses and corals: friends or anemonies?, and Virus in the O.K. Coral. 

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Guest Blogger, Molecular Virology

Zinc ionophores block the replication of nidovirus

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Contributed by guest blogger: Brian Lu ’13

Zinc ions function in many different cellular processes and have been shown to play important roles in the proper folding and activity of various cellular enzymes and transcription factors, but zinc ion concentrations are kept relatively low in the cell by metallothioneins. High concentration of zinc ions and compounds that stimulate cellular import of zinc ions have been shown to inhibit the replication of various RNA viruses, including influenza virus, respiratory syncytial virus, and several picornaviruses, but details of the effects of zinc ions on nidoviruses are not well understood. Nidoviruses include major pathogens of both human and livestock, including severe acute respiratory syndrome coronavirus (SARS-CoV), the arterivirus equine arteritis virus (EAV), and porcine reproductive and respiratory syndrome virus (PRRSV). A recent study suggests that zinc ions also inhibit nidovirus replication by blocking RNA synthesis.

 

As high concentrations of zinc is known to inhibit cellular translation, the researchers tested if high concentrations of zinc would also inhibit viral translation. After determining the concentration of pyrithione (PT) cells will tolerate without negative effects, cells were incubated with non-toxic concentrations of PT and zinc ions. PT, functioning as an ionophore, stimulated the cellular import of zinc ions and increased the cellular concentration of zinc. The results showed a dose-dependent inhibition of viral gene expression of both SARS-CoV and EAV by the addition of PT. The inhibition of viral gene expression appears to be the result of direct inhibition of RNA-dependent RNA polymerase (RdRp) activity. The researchers also observed a dose-dependent decrease in RNA synthesis for SARS-CoV and EAV by testing the effect of zinc on the virus’s replication/transcription complex (RTC). RNA synthesis, separate from mRNA synthesis for gene expression, is an integral part of viral replication, and a decrease in RNA synthesis would imply a decrease in viral replication as well. Interestingly, the zinc ion’s effects on RNA synthesis are reversible. The addition of magnesium-saturated ethylenediaminetetraacetic acid (MgEDTA) restored RTC activity in both EAV and SARS-CoV. MgEDTA ionizes to magnesium ions and EDTA in solution, which binds to the zinc ions and prevents them from interacting with viral RTC. Adding zinc ions at different stages of RNA synthesis showed that zinc inhibits synthesis at the initiation stage for EAV but inhibits synthesis at the initiation and elongation stages for SARS-CoV.

 

The use of zinc ions and PT as inhibitors of nidovirus replication in cell culture can be further investigated for use as antiviral compounds, and a better understanding of the inhibition mechanism may yield future antiviral drugs against SARS and other nidovirus-related diseases. But before zinc can be used as an antiviral compound, several questions need to be answered. What is the exact mechanism for RdRp inhibition? What are the systemic effects of PT? What levels of zinc and PT would be safe for an organism? The U.S. Food and Drug Administration has approved pyrithione zinc less than 2 percent in concentration for topical use in treating dandruff, but there are no guidelines for internal uses of pyrithione zinc. It is known, however, that industrial concentrations of PT zinc is highly toxic. Additionally, in depth structural analysis and mutational studies of nidovirus RdRps is needed to determine a structural mechanism for zinc-induced inhibition of RdRp activity. Unfortunately, zinc ion binding is very fleeting and not detectable with currently available methods.  As such, more sensitive methods of detecting zinc binding may be needed before the mechanism for zinc-induced inhibition of RdRp activity can be determined. Water-soluble zinc-ionophore may be better suited as the compound appears to be non-toxic even at concentrations that were effective against tumors in a mouse model. The reversible property of zinc-induced inhibition can be used in future research to gain a better understanding of nidoviral RNA synthesis. If pyrithione zinc is shown to be safe and effective in animal models, it still has to go through clinical trials before it can be used as an antiviral treatment.

Link:

http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1001176

Brian Lu is a junior at Vassar College, majoring in biochemistry.

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Guest Blogger, Immunology, Molecular Virology

Natural Resistance: How Your Genes Can Determine The Severity of Your Influenza Infection

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Contributed by guest blogger: Jared Saunders ’13

Every winter, the general public frantically agonizes over influenza prevention and protection. But is the purchase of hand sanitizer in bulk and tissue boxes by the dozen really necessary? After all, many people don’t even get sick during the winter months, and some just feel a little down for a couple of days. Why do some people catch “the flu” and end up in the hospital, fighting lung infections and plowing through boxes of tissues, while others just end up with a cough or runny nose? The answer may be come down to three letters. DNA.

Recent research by Everitt et al. at the Wellcome Trust Sanger Institute (WTSI) has revealed that a single gene found in humans can determine your fate when infected with a variety of the most common strains of the influenza virus. The gene encodes the important protein referred to as IFITM3, a member of the interferon-inducible transmembrane protein family. These IFITM proteins have been shown to potently restrict the replication of a variety of pathogenic viruses, and IFITM3 has been shown to greatly alter the course of influenza infection in both mice and humans.

Brass et al. previously identified IFITM3 through a functional genetic screen that indicated it mediated resistance to influenza A, dengue virus, and West Nile virus infection in vitro. This supported the hypothesis  of the WTSI group (more than 30 authors!), that IFITM proteins are critical for intrinsic resistance to these viruses, and allowed them to proceed with determining the effects of IFITM3 in vivo using mice. IFITM3 knockout mice showed severe signs of clinical illness, including massive body weight loss, rapid breathing, and piloerection (also known as “goosebumps”) when infected with low-pathogenecity strains of influenza that do not usually cause such intense symptoms. Their presentation of infection was more consistent with high-virulence strains of influenza. Contrary to the knockout mice, the wild-type mice shed significantly less of their body weight before fully recovering.

With this significant data now being collected, the group moved on to testing their hypothesis that individuals who are homozygous dominant for the IFITM3 gene develop less virulent influenza infections. They sequenced the IFITM3 gene from 53 people who were hospitalized by the H1N1 or seasonal influenza infection during 2009 to 2010 to determine if they carried the wild-type gene or one with some polymorphism. Genetic analysis of a subset of these individuals showed no evidence of hidden population structure differences with respect to a 1000 genome control group from WTSI. In the hospitalized patients, the group found significant over-representation of a specific single nucleotide polymorphism (or SNP), referred to as SNP rs12252, that has a recessive C allele substituted for a normal dominant T allele. This leads to an ineffective IFITM3 variant lacking the first 21 amino acids of the protein. This recessive C variant leads to lower IFITM3 expression in the host and consequent increased susceptibility of the host to influenza infection, and is correlated with lower levels of IFITM3 protein expression.

The group’s work has shown conclusively that IFITM3 expression can act as a barrier to influenza A virus infection both in vitro and in vivo, and that in vivo it can lower the mortality and morbidity associated with infection by a variety of human influenza viruses. Discovery of this innate resistance factor in humans may explain why encounters with a novel strain that may cause severe infections in others that do not affect you or your family.

But can the IFITM3 gene be used to help develop treatments or vaccines for future influenza strain outbreaks? Is it possible to recover this gene, if an individual has an ineffective variant, through gene therapy so as to make someone more resistant to influenza? With more research being done on the genetic aspects of disease infection, many more questions will arise, and many more answers will as well!

Links:

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature10921.html

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2824905/

Jared Saunders is a junior at Vassar College, majoring in biochemistry.

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Guest Blogger, Uncategorized

Fighting Fire with Fire: Using Poxviruses to Combat Cancer

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Contributed by guest blogger: Brooke Schieffer ’12

In September of last year, a group of researchers infected cancer patients with a genetically engineered poxvirus. While this may sound like something out of a horror movie, it is actually quite the opposite: Breitbach et al. were performing a clinical trial to explore new, innovative ways to treat cancer tumors. Some people may be put off by the idea of having live viruses injected into their blood stream, but it’s actually not that uncommon. Indeed, many vaccines are actually live viruses. In fact, the vaccinia virus used in this clinical trial was derived from a vaccine for smallpox.

However, creating an attenuated virus to use as a vaccine and creating a virus that selectively infects and destroys cancer cells are two very different things. Before the scientists can create tumor-killing viruses, they first need to make sure that the virus can infect cancer cells while ignoring normal tissue cells in our body. To do this, they genetically engineered a poxvirus, called JX-594, that could replicate only in cells harboring activation of epidermal growth factor (EGFR)/Ras pathway (many epithelial cancers rely on this pathway). The virus, however, does not lyse the cell as this was only a trial to explore the possibilities of selectively cancer infection, not destruction.

The virus itself was chosen for several different reasons. Firstly, vaccinia (and, consequently, JX-594) is well adapted to intravenous transportation and displays some resistance to antibody neutralization in the blood stream. It can also spread quickly within tissues, making it ideal for infecting tumors (especially solid metastatic tumors). Finally, JX-594 replication is dependent on a commonly activated signaling pathway in epithelial cancers: the EGFR/Ras pathway. Furthermore, to determine if JX-594 was selectively infecting and replicating within cancer cells, the researchers incorporated the lacZ transgene (which encodes β-galactosidase) into the viral genome. They then could track β-galactosidase expression via immunohistochemical staining or tagged antibodies to see where the viruses were replicating in human tissue.

To test the effects of their virus, Breitbach et al. conducted a clinical trial with 23 cancer patients by intravenously injecting them with different concentrations of JX-594. They found their results to be quite promising: in the higher dose groups, they observed selective infection in tumor cells and expression of the β-galactosidase protein. And all with little apparent side effects—the worst of which were symptoms typical of a 24-hour flu. This is the first experiment in which an intravenously injected virus was able to selectively replicate in tumor cells and express a transgene. Of course, this is just the first step on the road to effective treatment. First off, this was only a preliminary study to determine if the virus could selectively infect cancer cells, they did not engineer the virus to kill the cells yet. As of now, it is simply a possible delivery method, not a way to kill cancer cells. But the researchers are hopeful that viruses such as JX-594 will eventually be customizable with proteins or siRNA to treat different types of cancer.

However, there are still many questions to keep in mind moving forward. Will we be able to insert a gene into these viral vectors that only destroys tumor cells? Can this delivery system be modified to infect cancers that do not use the EGFR/Ras pathway? What about the possibility of viral mutations that would allow the virus to infect healthy tissue? And what about the immune system’s role? How will multiple treatments work given the fact that the immune system will build up immunity against the virus because it is invading the body? Even with these questions, this clinical trial was still an innovative and interesting new approach to cancer treatment.

Link:
http://www.nature.com/nature/journal/v477/n7362/full/nature10358.html#/affil-auth

Brooke Schieffer is a senior at Vassar College, majoring in Drama.

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Guest Blogger, Immunology, Molecular Virology

Polydnavirus: Good for the Parasitic Wasp, Bad for the Host Caterpillar

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Contributed by guest blogger: Jason Adler 

An endoparasitoid wasp would disagree with the popular perception of viruses as malevolent. Parasitoids are organisms that spend a substantial portion of their life cycle in the host; unlike a parasite, a parasitoid usually kills or sterilizes the host. Endoparasitoid wasp oviposit into the body cavity of caterpillars. When the wasp larvae emerges, it then consumes the host as it develops.

Polydnaviruses (PDV), a family of double stranded DNA insect viruses, are symbiotic to some endoparasitoid wasps. Of two PDV genera, genus Ichnovirus is specific to ichneumoid wasps and Bracovirus to braconid wasps. The PDV genome is located on host wasp chromosomes in a segmented, proviral form. However, the integrated PDV genome is not fully functional as it cannot replicate independent of the wasp and capsid proteins are non-existent.  It is unknown if PDV is derived from wasp genes or if ancestral wasps integrated a beneficial PDV into their genome with resulting loss of the genes responsible for capsid formation and virus replication.

As such, PDV only replicates at specific ovarian cells during the late pupal phase, where it acquires two viral envelopes. PDV integration does not occur in the viral life cycle; instead, the viral genome is vertically transmitted to wasp offspring during meiosis. When the female wasp injects her eggs into the lepidopteran host, virions are co-injected and result in infection. Although, PDV does not replicate in the host caterpillar, it does result in immunosuppression and alters the host development (i.e. prevents metamorphosis) and metabolism to favor the parasitoid larva. The normal response of lepidopteran larvae to small foreign material is phagocytosis, but larger pathogens must be encapsulated. This is accomplished through melanization, where certain hemocytes, invertebrate immune cells found in the hemolymph, secrete melanin, which surrounds the pathogen so that anti-microbial peptides can destroy it. When immune suppressed, host hemocytes do not destroy the wasp egg by forming hemocyte nodules. Thus, PDV and the wasp share a mutualistic relationship.

Cotesia plutellae, a braconid wasp, possesses a PDV – C. plutellae bracovirus (CpBV) – and parasitizes larvae of the diamond-back moth Plutella xylotsella. Recent research has found that CpBV encodes a viral histone H4 that shares high sequence homology with histone H4 on P. xylostella, except for the last 38 residues comprising the N-terminal tail. Additionally, this viral histone H4 N-terminal tail have been observed in other Cotesia-associated PDVs. It has been suggested that the N-terminal tail is altering gene expression regulation as viral H4 histones less easily detach from DNA than host H4 histones, thereby inhibiting transcription. Is the N-terminal tail of CpBV-H4 causing immunosuppression? The researchers hypothesized that the N-terminal tail is causing the suppression of antimicrobial peptide (AMP) genes.

To examine the effects of CpBV-H4, the researchers constructed two viral recombinants: a WT CpBV-H4 and a truncated CpBV-H4 that lacks the N-terminal tail. After injection of the viral vector into the host caterpillar, RT-PCR was used to look at the expression of putative AMP genes. Although basal expression levels were unchanged, when E. coli was introduced to the host to present an immune challenge CpBV-H4 inhibited inducible expression, while truncated CpBV-H4 did not. Additionally, by counting the number of melanized black nodules on the host caterpillar after injection of E. coli and the viral vector, the researchers assessed the immune response. While the larvae show hemocyte nodule formation in response to E. coli infection, transient expression of CpBV-H4 significantly suppressed the immune response by decreasing nodule formation, while truncated CpBV-H4 had no effect. Finally, the researchers examined a possible synergistic effect of CpBV-H4 and the entomopathogenic bacterium X. nematophila. Without CpBV-H4, X. nematophila infection resulted in low mortality; however, with CpBV-H4, there was significantly increased mortality with this synergistic effect lost if CpBV-H4 was truncated.

Based on these results, the researchers concluded that the N-terminal tail appears to be responsible for immunosuppression by inhibiting inducible expression of AMP genes, possibly by altering a normal epigenetic control. CpBV-H4 containing nucleosomes may less easily detach from DNA during transcription due to the increased positive charge resulting from the increased number of lysine residues in the N-terminal tail. By introducing a virus that expresses a viral H4 histone with a N-terminal tail, the parasitoid wasp is able to suppress the host immune system. This is important as without the immune suppression, the host hemocytes would encapsulate and destroy the wasp egg.

With 157 putative genes, CpBV is likely to have more than this one mechanism to suppress host immunity. Are there other mechanisms of CpBV immune suppression?  How else is the complex ecological relationship of wasp, virus, and caterpillar host mediated at the molecular level?

Link:

http://www.sciencedirect.com/science/journal/0006291X/415/2

Jason Adler is a senior at Vassar College, majoring in biology.

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Epidemics, Guest Blogger, Uncategorized

I Don’t Want Dengue Fever

When a student is absent from class, they usually send me an email to explain why. Occasionally I get emails from students in my microbiology or virology classes explaining their absence from class as a result of some infectious disease and they actually seem excited about the fact that they are hosting a virus. Perhaps they feel that they are participating in the class on a whole new level or are appreciating and understanding what is going on in their body, despite feeling awful. However, I was surprised recently when I mentioned Dengue Fever and a student piped up and said “I’ve had that!” I asked Caitlyn to write about her experience, and she kindly agreed. While she is interested in learning more about the virus, I suspect she would have preferred to learn about it without first hand experience. Here is her story.

Contributed by Caitlyn Anderson ’13

Photos of Angkor Wat in Siem Reap, Cambodia. Taken by Caitlyn Anderson.

“I was infected with Dengue virus in Cambodia during the summer of 2007 while working as an intern for the Clinton Foundation. I knew before going that there was a Dengue epidemic across the country but was unwilling to give up the opportunity. It is likely that I was bitten by a mosquito carrying the virus while I was sight seeing in Siem Reap towards the end of my stay. The virus incubated within my body for a period of approximately 5 days. Thankfully, I was back on U.S. soil when the virus began to present itself. I remember feeling slightly odd as I worked the night shift at Starbucks. After I returned home I immediately went to bed. In the morning I had developed flu like symptoms with a fever of 100 degrees. My body began to feel achy and I remained in bed throughout the afternoon. By 3:00 pm my temperature had reached 103 degrees and by 5:00 pm, my temperature was up to 104 degrees and I could barely move. My mother immediately called my pediatrician who then instructed us to go to the Emergency Room. I had immense difficulties walking from my bed on the second floor to the car. When we got to Norwalk Hospital in Connecticut, I was unable to walk and required the assistance of a wheel chair. The initial reaction of the emergency room doctor who saw to me first was that I was presenting with Lyme like symptoms. However, the unbearable pain caused by the insertion of the IV into my arm was not indicative of Lyme disease so I was immediately admitted to the hospital for further tests and supportive care. A few hours later my fever had reached 105 degrees and was coupled with the sudden onset of rash covering my entire body. The virus began to affect my nervous system causing extreme skin tenderness. Infectious disease specialists were brought in to evaluate my case. A Haitian doctor was immediately convinced I had Dengue Fever because she had witnessed the disease many times. Unsure of which of the four strains I had been infected with, the doctors could not predict the clinical evolution of the disease.
My fever remained between 103 and 105 degrees for 3 days. I was treated with fluid intravenously and pain medication for my body aches and severe skin sensitivity. My body was packed with ice in an effort to lower my body temperature. While Dengue Fever is commonly referred to as “breakbone fever” because people often feel as if there bones are being crushed, I did not experience this sensation. My skin, rather than my bones and joints, was the greatest cause of my discomfort. On day 4 of my hospital stay, my fever began to go down to 100 degrees but I was transitioned to the telemetry unit so that my heart could be monitored more closely. I continued to receive IV fluids and pain medication. I remained in the telemetry unit until day 6 when I was moved to a general ward where I remained until my release from the hospital on day 8. My fever had completely dissipated but I was very weak and had trouble walking. When I returned home I slept for 16 hours a day for about a week and was able to return to school a few days later with a reduced academic schedule. About a month later I regained my strength was symptom-free.”

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Epidemics, Evolution, Guest Blogger, Vaccines

Swine Flu: New and Improved!

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Contributed by guest blogger: Marni Hershbain ’11

Flu season is never enjoyable, but some seasons are certainly worse than others. The 2009 swine flu outbreak was particularly serious because the 2009 H1N1 strain was a novel virus, formed via the reassortment of swine, avian and human flu viruses. There were over 600,000 confirmed cases of H1N1 and over 18,449 deaths during the course of the pandemic. While this sounds pretty bad, it could have been much worse. The transmission efficiency of H1N1 was actually much lower than those of other pandemic strains, such as the 1918 H1N1 strain. Unfortunately, recent research demonstrates that this could change.

Flu strains are characterized by the hemagglutinin and neuraminidase found on their surfaces, hence names like H1N1. In order for the virus to infect a cell, hemagglutinin on the surface of the virus must bind to glycan receptors on the cell. Therefore, to explain the low transmission efficiency of 2009 H1N1, researchers looked to its hemagglutinin.
In most flu strains, the amino acids at positions 219 and 227 within the hemagglutinin are both hydrophobic or both charged. In 1918 H1N1 both are hydrophobic. However, the 2009 H1N1 strain has isolucine, a hydrophobic molecule, in position 219 and glutamic acid, a charged molecule, in position 227. Researchers hypothesized that lacking either hydrophobic or ionic interactions at these positions would disrupt the positioning of neighboring residues and decrease the hemagglutinin’s binding affinity. They further hypothesized that if they replaced isolucine with the charged amino acid lysine, stable inter-residue interactions would occur and binding affinity would increase.

When researchers compared the ability of wild type and isolucine→lysine mutant strains to bind to an array of glycans representing human binding sites, they found the binding ability of the mutant strain was 30 times greater. The mutant version also bound more intensely to receptors in human tracheal tissue. Researchers also infected ferrets (commonly used as models in human influenza studies) with either wild type or mutant virus. Only the ferrets infected with mutant virus spread the infection to all of the previously uninfected ferrets placed in close proximity to them.

The mutation of just one amino acid could greatly impact the transmission efficiency of 2009 H1N1. Flu viruses tend to mutate frequently, which is why a new vaccine needs to be developed every year. Predicting what these mutations will be is not an easy task, but mutations at the positions in this study will certainly be monitored closely.

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