While affecting all age groups, respiratory syncytial virus (RSV) infections can be particularly severe in infants, who develop functionally distinct immune responses, as well as in immunocompromised individuals. The extent to which environmental, viral and host factors contribute to the pathogenesis of RSV varies considerably between infected individuals. A correlation between the level of virus replication and pathogenesis has been established, and several viral proteins, in particular NS1 and NS2, modulate the immune response. Host immunity clearly contributes to RSV pathogenesis, and a number of specific cell populations may be involved. Ultimately, whether the response induced by RSV is protective or pathogenic depends on a combination of host factors, young age being one of the most important ones.
Although a number of different viruses cause “colds”, rhinoviruses are one of the most frequent sources. And although there are many serotypes of rhinovirus, they total number may not be enough to account for all the colds you get during your lifetime. A recent paper suggests that rhinoviruses are able to direct antibody responses away from the critical areas on the outside of the virus particle which give a neutralizing response towards internal regoins of the virus capsid not exposed to antibodies.
Misdirected antibody responses against an N-terminal epitope on human rhinovirus VP1 as explanation for recurrent RV infections. (2012) FASEB J. 26(3): 1001-1008
Rhinoviruses (RVs) are the primary cause of upper respiratory tract infections, generally known as the common cold. Moreover, RV infections can trigger severe exacerbations of asthma and chronic obstructive pulmonary disease (COPD). We expressed the 4 major RV capsid proteins, VP1-VP4, in Escherichia coli and used these proteins as well as recombinant and synthetic VP1 fragments to study and map antibody responses in RV-infected humans. VP1, which on infection binds to ICAM 1, was identified as a major target for the memory immune response, residing in the IgG1 subclass and IgA class. Interestingly, this response was mainly directed against an N-terminal 20mer peptide in VP1, P1a, which becomes exposed on intact RV only when it docks to its receptor ICAM 1. Molecular modeling using the 3-dimensional RV capsid structures revealed that P1a was localized inside the capsid and outside the areas involved in receptor binding or RV neutralization. Our results suggest misdirection of antibody responses against a nonprotective epitope as a mechanism how RV escapes immunity and causes recurrent infections. Based on these findings, it may be possible to design vaccines against RV infections and RV-induced respiratory diseases.
To put it bluntly, dengue virus is winning. We have so far failed in our attempts to make a safe and effective dengue virus vaccine, so we need alternatives. Recently, there has been emphasis on alternatives to vasccines (Should Science Pull the Trigger on Antiviral Drugs). A new paper looks at the biochemisty of dengue virus infection, knowledge that might lead us towards alternative strategies to fight this nasty virus.
Dengue Virus Infection Perturbs Lipid Homeostasis in Infected Mosquito Cells. (2012) PLoS Pathog 8(3): e1002584. doi:10.1371/journal.ppat.1002584
Dengue virus causes ~50–100 million infections per year and thus is considered one of the most aggressive arthropod-borne human pathogen worldwide. During its replication, dengue virus induces dramatic alterations in the intracellular membranes of infected cells. This phenomenon is observed both in human and vector-derived cells. Using high-resolution mass spectrometry of mosquito cells, we show that this membrane remodeling is directly linked to a unique lipid repertoire induced by dengue virus infection. Specifically, 15% of the metabolites detected were significantly different between DENV infected and uninfected cells while 85% of the metabolites detected were significantly different in isolated replication complex membranes. Furthermore, we demonstrate that intracellular lipid redistribution induced by the inhibition of fatty acid synthase, the rate-limiting enzyme in lipid biosynthesis, is sufficient for cell survival but is inhibitory to dengue virus replication. Lipids that have the capacity to destabilize and change the curvature of membranes as well as lipids that change the permeability of membranes are enriched in dengue virus infected cells. Several sphingolipids and other bioactive signaling molecules that are involved in controlling membrane fusion, fission, and trafficking as well as molecules that influence cytoskeletal reorganization are also up regulated during dengue infection. These observations shed light on the emerging role of lipids in shaping the membrane and protein environments during viral infections and suggest membrane-organizing principles that may influence virus-induced intracellular membrane architecture.
Currently, no vaccine exists for hepatitis C virus (HCV), a major pathogen thought to infect 170 million people globally. Many studies suggest that host T cell responses are critical for spontaneous resolution of disease, and preclinical studies have indicated a requirement for T cells in protection against challenge. Recent research aimed to elicit HCV-specific T cells with the potential for protection using a recombinant adenoviral vector strategy in a phase 1 study of healthy human volunteers.
Two adenovirus vectors expressing NS proteins from HCV genotype 1B were constructed based on rare serotypes [human adenovirus 6 (Ad6) and chimpanzee adenovirus 3 (ChAd3)]. Both vectors primed T cell responses against HCV proteins; these T cell responses targeted multiple proteins and were capable of recognizing heterologous strains (genotypes 1A and 3A). HCV-specific T cells consisted of both CD4+ and CD8+ T cell subsets; secreted interleukin-2, interferon-γ, and tumor necrosis factor–α; and could be sustained for at least a year after boosting with the heterologous adenoviral vector. Studies using major histocompatibility complex peptide tetramers revealed long-lived central and effector memory pools that retained polyfunctionality and proliferative capacity. These data indicate that an adenoviral vector strategy can induce sustained T cell responses of a magnitude and quality associated with protective immunity and open the way for studies of prophylactic and therapeutic vaccines for HCV.
HIV-1 has been analysed by structural biology techniques more than any other virus, with partial or complete structures known for all 15 of its protein components and additional structures determined for substrate- and host factor-bound complexes. Three-dimensional molecular structures can provide detailed information on biological mechanisms and, for cases in which the molecular function affects human health, can significantly aid in the development of therapeutic interventions.
For almost 25 years, key components of the lentivirus HIV-1, including the envelope glycoproteins, the capsid and the replication enzymes reverse transcriptase, integrase and protease, have been scrutinized to near atomic-scale resolution. Moreover, structural analyses of the interactions between viral and host cell components have yielded key insights into the mechanisms of viral entry, chromosomal integration, transcription and egress from cells. This review article discusses recent advances in HIV-1 structural biology, focusing on the molecular mechanisms of viral replication and on the development of new therapeutics:
Chlorella viruses are large, icosahedral, viruses with long double-stranded DNA genomes (Chlorella viruses (2006) Adv Virus Res. 66: 293-336). A new paper in PLoS ONE shows that the DNA genome of these viruses is packaged in such a way that when they contact a host cell, the force literally blows a hole in the cell wall and injects the genome into the cell:
Structural Organization of DNA in Chlorella Viruses. PLoS ONE 7(2): e30133. doi:10.1371/journal.pone.0030133
Chlorella viruses have icosahedral capsids with an internal membrane enclosing their large dsDNA genomes and associated proteins. Their genomes are packaged in the particles with a predicted DNA density of ca. 0.2 bp nm−3. Occasionally infection of an algal cell by an individual particle fails and the viral DNA is dynamically ejected from the capsid. This shows that the release of the DNA generates a force, which can aid in the transfer of the genome into the host in a successful infection. Imaging of ejected viral DNA indicates that it is intimately associated with proteins in a periodic fashion. The bulk of the protein particles detected by atomic force microscopy have a size of ~60 kDa and two proteins (A278L and A282L) of about this size are among 6 basic putative DNA binding proteins found in a proteomic analysis of DNA binding proteins packaged in the virion. A combination of fluorescence images of ejected DNA and a bioinformatics analysis of the DNA reveal periodic patterns in the viral DNA. The periodic distribution of GC rich regions in the genome provides potential binding sites for basic proteins. This DNA/protein aggregation could be responsible for the periodic concentration of fluorescently labeled DNA observed in ejected viral DNA. Collectively the data indicate that the large chlorella viruses have a DNA packaging strategy that differs from bacteriophages; it involves proteins and share similarities to that of chromatin structure in eukaryotes.
HIV-1 possesses a viral protein, integrase (IN), which is necessary for its efficient integration in target cells. However, it has been reported that an IN-defective HIV strain is still capable of integration. Here, we assessed the ability of wild type (WT) HIV-1 to establish infection in the presence of IN inhibitors. Researchers observed a low, yet clear infection of inhibitor-incubated cells infected with WT HIV which was identical to cells infected with IN-deficient HIV. The IN-independent integration could be enhanced by the pretreatment of cells with DNA-damaging agents suggesting that integration is mediated by a DNA repair system. Significantly faster viral replication kinetics with augmented viral DNA integration was observed after infection in irradiated cells treated with IN inhibitor compared to non-irradiated cells. These results suggest that HIV DNA has integration potential in the presence of an IN inhibitor and may serve as a virus reservoir.
One of the key features of viruses is that they are energy parasites, dependent on their host cells for the energy needed to replicate. This new research looks at ATP levels inside living cells where virus RNA is being replicated:
Visualization and Measurement of ATP Levels in Living Cells Replicating Hepatitis C Virus Genome RNA. (2012) PLoS Pathog 8(3): e1002561. doi:10.1371/journal.ppat.1002561
Adenosine 5′-triphosphate (ATP) is the primary energy currency of all living organisms and participates in a variety of cellular processes. Although ATP requirements during viral lifecycles have been examined in a number of studies, a method by which ATP production can be monitored in real-time, and by which ATP can be quantified in individual cells and subcellular compartments, is lacking, thereby hindering studies aimed at elucidating the precise mechanisms by which viral replication energized by ATP is controlled. In this study, we investigated the fluctuation and distribution of ATP in cells during RNA replication of the hepatitis C virus (HCV), a member of the Flaviviridae family. We demonstrated that cells involved in viral RNA replication actively consumed ATP, thereby reducing cytoplasmic ATP levels. Subsequently, a method to measure ATP levels at putative subcellular sites of HCV RNA replication in living cells was developed by introducing a recently-established Förster resonance energy transfer (FRET)-based ATP indicator, called ATeam, into the NS5A coding region of the HCV replicon. Using this method, we were able to observe the formation of ATP-enriched dot-like structures, which co-localize with non-structural viral proteins, within the cytoplasm of HCV-replicating cells but not in non-replicating cells. The obtained FRET signals allowed us to estimate ATP concentrations within HCV replicating cells as ~5 mM at possible replicating sites and ~1 mM at peripheral sites that did not appear to be involved in HCV replication. In contrast, cytoplasmic ATP levels in non-replicating Huh-7 cells were estimated as ~2 mM. To our knowledge, this is the first study to demonstrate changes in ATP concentration within cells during replication of the HCV genome and increased ATP levels at distinct sites within replicating cells. ATeam may be a powerful tool for the study of energy metabolism during replication of the viral genome.
Rabies is an preventable virus disease transmitted from infected animals to other warm blooded animals (zoonotic), especially human. Rabies occurs in more than 150 countries and territories. According to an estimation by WHO, almost 55,000 people die because of rabies every year. Dogs are the major reason behind this, approximately 99% human deaths caused by dog’s bites. Developing and under developing countries, both are the victims of rabies. With the post-exposure preventive regimes, 327,000 people can prevent this disease annually. This article is a short overview of the rabies virus genome, virology, symptoms, epidemiology, diagnostic methods, and the high risk countries around the globe.
While affecting all age groups, respiratory syncytial virus (RSV) infections can be particularly severe in infants, who develop functionally distinct immune responses, as well as in immunocompromised individuals. The extent to which environmental, viral and host factors contribute to the pathogenesis of RSV varies considerably between infected individuals. A correlation between the level of virus replication and pathogenesis has been established, and several viral proteins, in particular NS1 and NS2, modulate the immune response. Host immunity clearly contributes to RSV pathogenesis, and a number of specific cell populations may be involved. Ultimately, whether the response induced by RSV is protective or pathogenic depends on a combination of host factors, young age being one of the most important ones.
