Arunee Thitithanyanont

An Avian Influenza H5N1 Virus That Binds to a Human-Type Receptor

ABSTRACT Avian influenza viruses preferentially recognize sialosugar chains terminating in sialic acid-α2,3-galactose (SAα2,3Gal), whereas human influenza viruses preferentially recognize SAα2,6Gal. A conversion to SAα2,6Gal specificity is believed to be one of the changes required for the introduction of new hemagglutinin (HA) subtypes to the human population, which can lead to pandemics. Avian influenza H5N1 virus is a major threat for the emergence of a pandemic virus. As of 12 June 2007, the virus has been reported in 45 countries, and 312 human cases with 190 deaths have been confirmed. We describe here substitutions at position 129 and 134 identified in a virus isolated from a fatal human case that could change the receptor-binding preference of HA of H5N1 virus from SAα2,3Gal to both SAα2,3Gal and SAα2,6Gal. Molecular modeling demonstrated that the mutation may stabilize SAα2,6Gal in its optimal cis conformation in the binding pocket. The mutation was found in approximately half of the viral sequences directly amplified from a respiratory specimen of the patient. Our data confirm the presence of H5N1 virus with the ability to bind to a human-type receptor in this patient and suggest the selection and expansion of the mutant with human-type receptor specificity in the human host environment.

High Susceptibility of Human Dendritic Cells to Avian Influenza H5N1 Virus Infection and Protection by IFN-α and TLR Ligands

There is worldwide concern that the avian influenza H5N1 virus, with a mortality rate of >50%, might cause the next influenza pandemic. Unlike most other influenza infections, H5N1 infection causes a systemic disease. The underlying mechanisms for this effect are still unclear. In this study, we investigate the interplay between avian influenza H5N1 and human dendritic cells (DC). We showed that H5N1 virus can infect and replicate in monocyte-derived and blood myeloid DC, leading to cell death. These results suggest that H5N1 escapes viral-specific immunity, and could disseminate via DC. In contrast, blood pDC were resistant to infection and produced high amounts of IFN-α. Addition of this cytokine to monocyte-derived DC or pretreatment with TLR ligands protected against infection and the cytopathic effects of H5N1 virus.

Indigenous sources of 2007–2008 H5N1 avian influenza outbreaks in Thailand

Outbreaks of H5N1 avian influenza show strong seasonality. It is not clear where the source of virus originates from in each new outbreak season. This study sought to understand the nature of viral resurgence in recent outbreak seasons in Thailand, where the epidemic is relatively well controlled. In such a situation, indigenous viruses surviving the inter-outbreak season would have to pass through a bottleneck. In order to look for evidence of the bottleneck effect, viral genome sequences from recent outbreaks in the country were analysed. H5N1 avian influenza viruses were isolated from six outbreaks in the rainy season and winter of 2007 through to early 2008. Most of the outbreaks were in the Yom-Nan River basin in the southern part of the northern region of the country. Sequences of these viral isolates were identified as clade 1, genotype Z, similar to viruses from previous years in the central region of the country. The sequences clustered into two groups, one of which was closely related to viruses isolated from the same area in July 2006. These analyses indicated that there was a strong bottleneck effect on the virus population and that only a few lineages remained in the area. In addition, evidence of reassortment among these viruses was found. These indicated re-emergence of viruses from a small pool of indigenous sources that had been silently perpetuated over the dry summer months. Therefore, an approach to eradicate H5N1 avian influenza from the area by eliminating these local reservoirs may be feasible and should be seriously considered.

A simple screening assay for receptor switching of avian influenza viruses

BACKGROUND Adaptation of the receptor-binding preference from alpha2,3- to alpha2,6-linked sialic acid is an essential step for an avian influenza virus to transmit efficiently in human population and become a pandemic virus. The currently available assays for receptor-binding preference are complex and not widely available. OBJECTIVES A simple high-throughput screening assay will facilitate early detection of a potential pandemic virus, which is crucial for the prevention and control of the possible pandemic. We wanted to develop a simple assay to differentiate influenza viruses with alpha2,3- or alpha2,6-linked receptor-binding preference. STUDY DESIGN The assay employs a specific sialidase (from Salmonella thyphimurium) that can eliminate alpha2,3-linked sialic acid from red blood cells. A reduction of hemagglutination titer indicates alpha2,3-linked receptor preference in this assay. RESULTS Using a panel of H5N1 avian influenza isolates and H1/H3 human influenza isolates, as well as mutated H5 reverse genetics virus, the assay could accurately differentiate the viruses according to their receptor-binding preference. Furthermore, the assay was sufficiently sensitive to detect a minor variant with alpha2,6-linkage-specificity in a background of alpha2,3-linkage-specific virus. CONCLUSIONS We have developed a simple screening assay capable of detecting avian influenza viruses that have switched their receptor-binding preference.

Influenza A virus molecularly imprinted polymers and their application in virus sub-type classification

In this work, we apply a molecular imprinting strategy as a screening protocol for different influenza A subtypes, namely H5N1, H5N3, H1N1, H1N3 and H6N1. Molecularly imprinted polymers for each of these subtypes lead to appreciable sensor characteristics on a quartz crystal microbalance leading to detection limits as low as 105 particles per ml. Selectivity studies indicate that each virus is preferably incorporated by its own MIP. Recognition in most cases is dominated by the neuraminidase residue rather than the hemagglutinin. Multivariate analysis shows that the sensor responses can be correlated with the differences in hemagglutinin and neuraminidase patterns from databases. This allows for virus subtype characterization and thus rapid screening.

Apoptosis induced by avian H5N1 virus in human monocyte-derived macrophages involves TRAIL-inducing caspase-10 activation.

Avian influenza virus H5N1 is a potentially fatal disease not only in birds, but also in humans. The virus is able to induce apoptosis in many cell types including macrophages and dendritic cells. In the present study, we demonstrated that TNF-related apoptosis-inducing ligand (TRAIL) is involved in apoptosis-associated mechanisms of apoptosis downstream of the TRAIL receptor in H5N1 virus-infected human monocyte-derived macrophages (MDMs). Activation of caspase-10 was also observed in avian virus H5N1-infected MDMs. In the presence of caspase-10 inhibitor, Z-AEVD-FMK, the activation of Bid and a release of apoptotic-inducing factor (AIF) from mitochondria were markedly reduced, resulting in a significant decrease of apoptotic cells which suggested the involvement of caspase-10 activation in mitochondria leakage. Furthermore, neutralizing Ab against TRAIL significantly reduced caspase-10 activities, which paralleled with a decrease in the number of apoptotic cells. Together, this study demonstrated that apoptosis in avian virus H5N1-infected MDMs was induced by TRAIL-activated caspase-10, resulting in the activation of Bid and the release of AIF from mitochondria.

Antiviral immune responses in H5N1-infected human lung tissue and possible mechanisms underlying the hyperproduction of interferon-inducible protein IP-10.

Information on the immune response against H5N1 within the lung is lacking. Here we describe the sustained antiviral immune responses, as indicated by the expression of MxA protein and IFN-alpha mRNA, in autopsy lung tissue from an H5N1-infected patient. H5N1 infection of primary bronchial/tracheal epithelial cells and lung microvascular endothelial cells induced IP-10, and also up-regulated the retinoic acid-inducible gene-I (RIG-I). Down-regulation of RIG-I gene expression decreased IP-10 response. Co-culturing of H5N1-infected pulmonary cells with TNF-alpha led to synergistically enhanced production of IP-10. In the absence of viral infection, TNF-alpha and IFN-alpha also synergistically enhanced IP-10 response. Methylprednisolone showed only a partial inhibitory effect on this chemokine response. Our findings strongly suggest that both the H5N1 virus and the locally produced antiviral cytokines; IFN-alpha and TNF-alpha may have an important role in inducing IP-10 hyperresponse, leading to inflammatory damage in infected lung.

Qualitative detection of avian influenza A (H5N1) viruses: A comparative evaluation of four real-time nucleic acid amplification methods

The aim of this study was to determine the performance of real-time amplification based methods - NASBA, TaqMan, RT-FRET, and RT-PCR LUXtrade mark formats - for the detection of influenza A (H5N1) virus RNA. In an analysis of 54 samples obtained from a range of animal species in Thailand during the period 2003-2006, results showed that the NASBA (H5=98.2%, N1=96.3%), TaqMan (H5=98.2%, N1=96.3%) and FRET (H5=98.2%, N1=96.3%) had significantly higher rates of positive detection than LUX (H5=94.4%, N1=50.0%; P<0.001) for influenza A, H5 and N1 isolates. There were no false-positive results from any methods used in the negative-control group of samples. The limits of analytical detection were at least 10copies/reaction in real-time NASBA and LUX assays, while FRET and TaqMan assay appeared to be less sensitive at > or =100copies/reaction. The assays were relatively specific without cross-reactivity to a number of other influenza strains or viral pathogens. In conclusion, our study demonstrated that real-time NASBA, TaqMan and FRET assays can be used to detect influenza A (H5N1) from a wide range of hosts, and be specific for H5N1 samples obtained during different outbreaks (2003-2006). All assays provided the benefit of rapid influenza H5N1 identification for early diagnosis, in the range of hours, and they are well suited to high throughput analyses.

Generating and characterizing monoclonal and polyclonal antibodies against avian H5N1 hemagglutinin protein.

Accurate and timely diagnoses are central to H5N1 infection control. Here we describe the cloning and expression of the HA1 protein of the A/Vietnam/1203/04 strain in a bacterial system to generate mono-/polyclonal antibodies. All of the eight generated monoclonal antibodies recognized the same linear epitope on the top globular region of the HA structure -- a highly conserved epitope among all circulating H5N1 clades identified by amino acid alignment. Results from immunofluorescence staining and Western blotting indicate that all monoclonal antibodies interacted with a denatured form of HA proteins, while the resultant polyclonal antibodies recognized both denatured and native HA proteins on H5N1 reverse-genetics (RG) viruses. Results from flow cytometry and microneutralization assays indicate that the polyclonal antibodies blocked viral binding and neutralized H5N1-RG viruses. Our results may prove useful to establishing future H5N1 mono-and polyclonal antibodies, and perhaps contribute to the development of an alternative H5N1 vaccine.

HLA-associated immune pressure on Gag protein in CRF01_AE-infected individuals and its association with plasma viral load.

Background The human leukocyte antigen (HLA)-restricted cytotoxic T-lymphocyte (CTL) immune response is one of the major factors determining the genetic diversity of human immunodeficiency virus (HIV). There are few population-based analyses of the amino acid variations associated with the host HLA type and their clinical relevance for the Asian population. Here, we identified HLA-associated polymorphisms in the HIV-1 CRF01_AE Gag protein in infected married couples, and examined the consequences of these HLA-selected mutations after transmission to HLA-unmatched recipients. Methodology/Principal Findings One hundred sixteen HIV-1-infected couples were recruited at a government hospital in northern Thailand. The 1.7-kb gag gene was amplified and directly sequenced. We identified 56 associations between amino acid variations in Gag and HLA alleles. Of those amino acid variations, 35 (62.5%) were located within or adjacent to regions reported to be HIV-specific CTL epitopes restricted by the relevant HLA. Interestingly, a significant number of HLA-associated amino acid variations appear to be unique to the CRF01_AE-infected Thai population. Variations in the capsid protein (p24) had the strongest associations with the viral load and CD4 cell count. The mutation and reversion rates after transmission to a host with a different HLA environment varied considerably. The p24 T242N variant escape from B57/58 CTL had a significant impact on the HIV-1 viral load of CRF01_AE-infected patients. Conclusions/Significance HLA-associated amino acid mutations and the CTL selection pressures on the p24 antigen appear to have the most significant impact on HIV replication in a CRF01_AE-infected Asian population. HLA-associated mutations with a low reversion rate accumulated as a footprint in this Thai population. The novel HLA-associated mutations identified in this study encourage us to acquire more extensive information about the viral dynamics of HLA-associated amino acid polymorphisms in a given population as effective CTL vaccine targets.