Chikungunya virus (CHIKV) is transmitted by Aedes mosquitoes and causes Chikungunya fever. CHIKV occurs in the tropical and subtropical parts of the world. Regions where it has already caused epidemics include Africa, territories around the Indian Ocean, Southeast Asia, and meanwhile also the Caribbean, Central America, and South America. Around 1.2 million people are estimated to be infected so far during an epidemic in America. Since the Aedes albopictus mosquito, also known as Asian tiger mosquito, has now reached southern Europe and the USA, we are faced with further spreading of the virus.
Chikungunya fever is characterized by fever and severe joint pain, hence its name, which means “that which bends up”. In 30 to 40 percent of the cases, these joint pains can last several months or even up to several years. Attempts at developing suitable vaccines have up to now been unsuccessful. To develop an effective vaccine, it is nessecary to identify a suitable antigen structure of the virus which will create an effective immune response in humans. Previous approaches have used the entire E2 surface protein as a basis for the vaccine, partly in combination with other virus proteins. These proteins, however, have a relatively large structure, which would make commercial vaccine production difficult.
A new paper investigates whether smaller more specific and less complex parts of E2 would suffice for generating a protective immune response. Based on the three-dimensional structure of the protein, researchers selected different areas exposed on the surface to joined them together, creating several artificial protein fragments. After production in E. coli and purification, mice were immunized with these protein fragments, and their blood was examined for neutralizing antibodies later on. In this experiment, one fragment, described as sAB+, proved to be the most effective one to induce neutralizing antibodies. It was used to immunize mice which were then infected by the wild-type Chikungunya virus. Compared with non-vaccinated animals, the mice treated showed significantly less virus RNA in the blood – a sign of partial immune protection.
A Small Antigenic Determinant of the Chikungunya Virus E2 Protein Is Sufficient to Induce Neutralizing Antibodies which Are Partially Protective in Mice. (2015) PLoS Negl Trop Dis 9(4): e0003684. doi:10.1371/journal.pntd.0003684
Macrophages destroy bacteria by engulfing them in intracellular compartments, which they then acidify to kill or neutralize the bacteria. However, some pathogenic bacteria, such as Salmonella enterica, have evolved to exist and even grow while within these acidified compartments. How Salmonella responds to the acidic environment and how that environment affects the virulence of this pathogen are unclear.
A new paper in in PLOS Biology demonstrate thats, instead of combating the acidification of the Salmonella-containing vacuole, Salmonella acidifies its own cytoplasm in response to the extracellular low pH (A FRET-Based DNA Biosensor Tracks OmpR-Dependent Acidification of Salmonella during Macrophage Infection. doi: 10.1371/journal.pbio.1002116). The acidic cytoplasm then acts as a signal to stimulate the secretion of a particular class of Salmonella virulence proteins. These virulence proteins, or effectors, are released into the host cell, where they are able to perturb the immune response.
The findings of this paper contradict other previous reports that suggest that a neutralization step is required for secretion of the virulence proteins. The authors show that Salmonella has adapted what was once an antibacterial response by the macrophage into a signal for when it is in the correct time and place to secret its virulence proteins and establish an infection.
How Salmonella Survives the Macrophage’s Acid Attack. (2015) PLoS Biol 13(4): e1002117. doi:10.1371/journal.pbio.1002117
Human hepatitis B virus (HBV) is the prototype of a family of small DNA viruses that productively infect hepatocytes, the major cell of the liver, and replicate by reverse transcription of a terminally redundant viral RNA, the pregenome. Upon infection, the circular, partially double-stranded virion DNA is converted in the nucleus to a covalently closed circular DNA (cccDNA) that assembles into a minichromosome, the template for viral mRNA synthesis. Infection of hepatocytes is non-cytopathic. Infection of the liver may be either transient (<6 months) or chronic and lifelong, depending on the ability of the host immune response to clear the infection. Chronic infections can cause immune-mediated liver damage progressing to cirrhosis and hepatocellular carcinoma (HCC). The mechanisms of carcinogenesis are unclear. Antiviral therapies with nucleoside analog inhibitors of viral DNA synthesis delay sequelae, but cannot cure HBV infections due to the persistence of cccDNA in hepatocytes.
Molecular biology of hepatitis B virus infection. Virology. 07 March 2015. doi: 10.1016/j.virol.2015.02.031
Most yeast prions (infectious proteins) are amyloids, linear β-sheet-rich polymers of a single protein with the β-strands perpendicular to the long axis of the filament. A single prion protein can form any of many different prion variants, differing in structure and biological properties, but with the same amino acid sequence. The folded parallel β-sheet architecture shown for several yeast prions explains how a given prion variant can be propagated stably, how a protein can template its conformation, just as DNA can template its sequence.
A recent paper in PLoS Pathogens describes an anti-prion system that sequesters prion seeds, preventing their even distribution to daughter cells. The recent discovery of a cellular anti-prion system that cures most arising prions of the yeast Ure2 protein offers a possible direction to look for treatments of amyloidoses such as Alzheimer disease, Parkinson disease, and others. While an array of methods have been found to cure yeast prions by over- or underproduction of various chaperones and other proteins and by various conditions, the system described in this paper cures the [URE3] prion at normal expression levels, indicating that this is a cellular anti-prion system. Information gleaned from yeast systems may have applications in efforts to control human prions and amyloidoses.
Yeast Prions: Proteins Templating Conformation and an Anti-prion System. (2015) PLoS Pathog 11(2): e1004584. doi:10.1371/journal.ppat.1004584
Approximately 10.8% of human cancers are associated with infection by an oncogenic virus. These viruses include human papillomavirus (HPV), Epstein–Barr virus (EBV), Merkel cell polyomavirus (MCV), human T-cell leukemia virus 1 (HTLV-1), Kaposi’s sarcoma-associated herpesvirus (KSHV), hepatitis C virus (HCV) and hepatitis B virus (HBV). These oncogenic viruses, with the exception of HCV, require the host RNA splicing machinery in order to exercise their oncogenic activities, a strategy that allows the viruses to efficiently export and stabilize viral RNA and to produce spliced RNA isoforms from a bicistronic or polycistronic RNA transcript for efficient protein translation. Infection with a tumor virus affects the expression of host genes, including host RNA splicing factors, which play a key role in regulating viral RNA splicing of oncogene transcripts. A current prospective focus is to explore how alternative RNA splicing and the expression of viral oncogenes take place in a cell- or tissue-specific manner in virus-induced human carcinogenesis.
Oncogenes and RNA splicing of human tumor viruses. (2014) Emerging Microbes & Infections, 3(9), e63
The genus Morbillivirus belongs to the virus family Paramyxoviridae, a group of enveloped viruses with non-segmented, negative strand RNA genomes. It contains viruses that are highly infectious, spread via the respiratory route, cause profound immune suppression, and have a propensity to cause large outbreaks associated with high morbidity and mortality in previously unexposed populations. In populations with endemic virus circulation, the epidemiology changes to that of a childhood disease, as hosts that survive the infection normally develop lifelong immunity.
Research on morbillivirus infections has led to exciting developments in recent years. Global measles vaccination coverage has increased, resulting in a significant reduction in measles mortality. In 2011 rinderpest virus was declared globally eradicated – only the second virus to be eradicated by targeted vaccination. Identification of new cellular receptors and implementation of recombinant viruses expressing fluorescent proteins in a range of model systems have provided fundamental new insights into the pathogenesis of morbilliviruses, and their interactions with the host immune system. Nevertheless, both new and well-studied morbilliviruses are associated with significant disease in wildlife and domestic animals. This illustrates the need for robust surveillance and a strategic focus on barriers that restrict cross-species transmission. Recent and ongoing measles outbreaks also demonstrate that maintenance of high vaccination coverage for these highly infectious agents is critical. This article summarizes the most important current research topics in this field.
The identification of cellular receptors and improvement of animal models has provided important new insights into the pathogenesis of morbillivirus infections. It has become clear that all morbilliviruses initially infect cells of the immune system, before they spread to epithelial, endothelial and/or neuronal cells. Morbilliviruses remain a potential cause of disease outbreaks in previously unexposed populations. However, they can also be used to our advantage, as vaccine vectors or as oncolytic viruses. Sustained vaccination coverage and surveillance of circulating morbilliviruses will remain of critical importance for years to come.
Morbillivirus Infections: An Introduction. (2015) Viruses 7(2): 699-706. doi: 10.3390/v7020699
Free online book:
- Part 1: Filters and Discovery
- Part 2: The Ultracentrifuge, Eggs and Flu
- Part 3: Phages, Cell Culture and Polio
- Part 4: RNA Genomes and Modern Virology
Edward P Rybicki and Russell Kightley (2015) A Short History of the Discovery of Viruses
This review discusses the structural and mechanistic basis of innate immune antagonism by two direct effectors, the Rotavirus NSP1 and VP3 proteins. It starts with a nice overview of Rotavirus biology then goes on to describe how the structural and mechanistic properties of NSP1 and VP3 allow these proteins to directly antagonize host innate immune responses.
NSP1 is a putative E3 ubiquitin ligase that mediates the degradation of a wide range of cellular targets, including those that function as innate immune sensors (RIG-I), signaling intermediates (TRAF2, MAVS, and β-TrCP), transcription factors (IRFs), and mediators of host survival pathways (PI3K and p53). In many respects, VP3 is like two proteins in one: it caps viral transcripts as they emerge from RV DLPs, which likely prevents activation of host RNA sensors, and it directly antagonizes the dsRNA-responsive OAS/RNase L pathway by cleaving the signaling molecule 2-5A. VP3 may also function in two distinct regions of the cell during infection: within a viral particle as the capping enzyme and perhaps also within the cytoplasm as a direct innate immune antagonist.
The varied functions of NSP1 and VP3 highlight the diversity and importance of cellular innate immune defenses to RNA viruses and reflect the compactness of a viral genome.
Silencing the alarms: Innate immune antagonism by rotavirus NSP1 and VP3. Virology. 24 Feb 2015 doi: 10.1016/j.virol.2015.01.006
TThe innate immune response involves a broad array of pathogen sensors that stimulate the production of interferons (IFNs) to induce an antiviral state. Rotavirus, a significant cause of childhood gastroenteritis and a member of the Reoviridae family of segmented, double-stranded RNA viruses, encodes at least two direct antagonists of host innate immunity: NSP1 and VP3. NSP1, a putative E3 ubiquitin ligase, mediates the degradation of cellular factors involved in both IFN induction and downstream signaling. VP3, the viral capping enzyme, utilizes a 2H-phosphodiesterase domain to prevent activation of the cellular oligoadenylate synthase (OAS)/RNase L pathway. Computational, molecular, and biochemical studies have provided key insights into the structural and mechanistic basis of innate immune antagonism by NSP1 and VP3 of group A rotaviruses (RVA). Future studies with non-RVA isolates will be essential to understand how other rotavirus species evade host innate immune responses.