Characterization of human transcription factor function and patterns of gene regulation in HepG2 cells

Transcription factors (TFs) are trans-acting proteins that bind cis-regulatory elements (CREs) in DNA to control gene expression. Here, we analyzed the genomic localization profiles of 529 sequence-specific TFs and 151 cofactors and chromatin regulators in the human cancer cell line HepG2, for a total of 680 broadly termed DNA-associated proteins (DAPs). We used this deep collection to model each TF's impact on gene expression, and identified a cohort of 26 candidate transcriptional repressors. We examine high occupancy target (HOT) sites in the context of three-dimensional genome organization and show biased motif placement in distal-promoter connections involving HOT sites. We also found a substantial number of closed chromatin regions with multiple DAPs bound, and explored their properties, finding that a MAFF/MAFK TF pair correlates with transcriptional repression. Altogether, these analyses provide novel insights into the regulatory logic of the human cell line HepG2 genome and show the usefulness of large genomic analyses for elucidation of individual TF functions.

Deleterious, protein-altering variants in the transcriptional coregulator ZMYM3 in 27 individuals with a neurodevelopmental delay phenotype

Neurodevelopmental disorders (NDDs) result from highly penetrant variation in hundreds of different genes, some of which have not yet been identified. Using the MatchMaker Exchange, we assembled a cohort of 27 individuals with rare, protein-altering variation in the transcriptional coregulator ZMYM3, located on the X chromosome. Most (n = 24) individuals were males, 17 of which have a maternally inherited variant; six individuals (4 male, 2 female) harbor de novo variants. Overlapping features included developmental delay, intellectual disability, behavioral abnormalities, and a specific facial gestalt in a subset of males. Variants in almost all individuals (n = 26) are missense, including six that recurrently affect two residues. Four unrelated probands were identified with inherited variation affecting Arg441, a site at which variation has been previously seen in NDD-affected siblings, and two individuals have de novo variation resulting in p.Arg1294Cys (c.3880C>T). All variants affect evolutionarily conserved sites, and most are predicted to damage protein structure or function. ZMYM3 is relatively intolerant to variation in the general population, is widely expressed across human tissues, and encodes a component of the KDM1A-RCOR1 chromatin-modifying complex. ChIP-seq experiments on one variant, p.Arg1274Trp, indicate dramatically reduced genomic occupancy, supporting a hypomorphic effect. While we are unable to perform statistical evaluations to definitively support a causative role for variation in ZMYM3, the totality of the evidence, including 27 affected individuals, recurrent variation at two codons, overlapping phenotypic features, protein-modeling data, evolutionary constraint, and experimentally confirmed functional effects strongly support ZMYM3 as an NDD-associated gene.

Quality standards and guidelines for test validation for infectious diseases in veterinary laboratories

The World Organisation for Animal Health Manual of Diagnostic Tests and Vaccines for Terrestrial Animals, Chapter 1.1.1. summarises the most relevant governance and managerial aspects of veterinary testing laboratories, and Chapter 1.1.5. introduces quality management. Both chapters are based on the International Organization for Standardization/International Electrotechnical Commission standard, ISO/IEC 17025:2005 'General requirements for the competence of testing and calibration laboratories'. This paper provides an update of standards and regulatory bodies relevant for accreditation of quality management systems (QMS), with a focus on ISO/IEC 17025:2017 for testing and calibration laboratories. Important issues and considerations that a laboratory should address in the design and maintenance of its QMS are highlighted and examples provided, in particular aspects of test validation and verification, including measurement uncertainty (MU). A QMS aims to address all aspects of the laboratory operation, including staff, organisational structure, processes, and procedures. Accreditation of a diagnostic laboratory requires three notable components: (a) independent or third-party assessment; (b) suitably validated tests performed by proficient laboratory operators in an adequately equipped laboratory; and (c) ongoing internal and external quality control. Together, these components ensure a test outcome is the result of a standardised process and structured peer review, and demonstrate both competency and ability to produce technically valid diagnostic results that will meet the needs of customers - veterinarians, animal owners, regulators, organisations and industry - as well as the needs of decision-makers involved in animal health and surveillance programmes.

Your assay has changed - is it still 'fit for purpose'? What evaluation is required

A reliable laboratory assay is an essential tool for the diagnosis or surveillance of most animal diseases. Before routine use, assays should be appropriately validated to ensure that they have performance characteristics that provide reliable results and can be used for the intended purpose. It is inevitable that, over time, changes will need to be made to assay reagents, to the assay format, to test a different species or for implementation in a new laboratory. Whenever there is a change (whether it be components, application or location), it is essential to establish whether the new circumstances affect the biological basis and properties of the assay. If the modifications do not affect the biological basis of the assay, the changes might be considered minor and a verification study can be conducted to confirm that the performance characteristics have not been adversely affected. Major changes require a new validation to be carried out. A method comparability study, where original and modified assays are run concurrently to test the same sample panel, provides an extremely robust comparison. However, comparability studies are not always an option, especially for the introduction of a method to a new laboratory. Access to original validation data and suitable reference sample panels then becomes essential to provide evidence that the assay remains 'fit for the intended purpose'.

Genome-wide strand asymmetry in massively parallel reporter activity favors genic strands

Massively parallel reporter assays (MPRAs) are useful tools to characterize regulatory elements in human genomes. An aspect of MPRAs that is not typically the focus of analysis is their intrinsic ability to differentiate activity levels for a given sequence element when placed in both of its possible orientations relative to the reporter construct. Here, we describe pervasive strand asymmetry of MPRA signals in data sets from multiple reporter configurations in both published and newly reported data. These effects are reproducible across different cell types and in different treatments within a cell type and are observed both within and outside of annotated regulatory elements. From elements in gene bodies, MPRA strand asymmetry favors the sense strand, suggesting that function related to endogenous transcription is driving the phenomenon. Similarly, we find that within Alu mobile element insertions, strand asymmetry favors the transcribed strand of the ancestral retrotransposon. The effect is consistent across the multiplicity of Alu elements in human genomes and is more pronounced in less diverged Alu elements. We find sequence features driving MPRA strand asymmetry and show its prediction from sequence alone. We see some evidence for RNA stabilization and transcriptional activation mechanisms and hypothesize that the effect is driven by natural selection favoring efficient transcription. Our results indicate that strand asymmetry is a pervasive and reproducible feature in MPRA data. More importantly, the fact that MPRA asymmetry favors naturally transcribed strands suggests that it stems from preserved biological functions that have a substantial, global impact on gene and genome evolution.

Occupancy maps of 208 chromatin-associated proteins in one human cell type

Transcription factors are DNA-binding proteins that have key roles in gene regulation^1,2. Genome-wide occupancy maps of transcriptional regulators are important for understanding gene regulation and its effects on diverse biological processes^3–6. However, only a minority of the more than 1,600 transcription factors encoded in the human genome has been assayed. Here we present, as part of the ENCODE (Encyclopedia of DNA Elements) project, data and analyses from chromatin immunoprecipitation followed by high-throughput sequencing (ChIP–seq) experiments using the human HepG2 cell line for 208 chromatin-associated proteins (CAPs). These comprise 171 transcription factors and 37 transcriptional cofactors and chromatin regulator proteins, and represent nearly one-quarter of CAPs expressed in HepG2 cells. The binding profiles of these CAPs form major groups associated predominantly with promoters or enhancers, or with both. We confirm and expand the current catalogue of DNA sequence motifs for transcription factors, and describe motifs that correspond to other transcription factors that are co-enriched with the primary ChIP target. For example, FOX family motifs are enriched in ChIP–seq peaks of 37 other CAPs. We show that motif content and occupancy patterns can distinguish between promoters and enhancers. This catalogue reveals high-occupancy target regions at which many CAPs associate, although each contains motifs for only a minority of the numerous associated transcription factors. These analyses provide a more complete overview of the gene regulatory networks that define this cell type, and demonstrate the usefulness of the large-scale production efforts of the ENCODE Consortium.

ChIP–seq and CETCh–seq data are used to analyse binding maps for 208 transcription factors and other chromatin-associated proteins in a single human cell type, providing a comprehensive catalogue of the transcription factor landscape and gene regulatory networks in these cells.

Differential effects of knowledge and aging on the encoding and retrieval of everyday activities

We deconstruct continuous streams of action into smaller, meaningful events. Research has shown that the ability to segment continuous activity into such events and remember their contents declines with age; however, knowledge improves with age. We investigated how young and older adults use knowledge to more efficiently encode and later remember information from everyday events by having participants view a series of self-paced slideshows depicting everyday activities. For some activities, older adults produce more normative scripts than do young adults (older adult activities) and for other activities, young adults produce more normative scripts than do older adults (young adult activities). Overall, participants viewed event boundaries longer than within events (i.e., the event boundary advantage) replicating prior research (e.g., Hard, Recchia, & Tversky, 2011). Importantly, older adults demonstrated the boundary advantage for the older adult activities but not the young adult activities, and they also had better recognition memory for the older adult activities than the young adult activities. We also found that the magnitude of a participant's boundary advantage was associated with better memory, but only for the less knowledgeable activities. Results indicate that older adults use their intact knowledge to better encode and remember everyday activities, but that knowledge and event segmentation may have independent influences on event memory.

Epitope Tagging ChIP-Seq of DNA Binding Proteins Using CETCh-Seq

Chromatin immunoprecipitation followed by next-generation DNA sequencing (ChIP-seq) has been used to identify transcription factor (TF) binding proteins throughout the genome. Unfortunately, this approach traditionally requires commercially available, ChIP-seq grade antibodies that frequently fail to generate acceptable datasets. To obtain data for the many TFs for which there is no appropriate antibody, we recently developed a new method for performing ChIP-seq by epitope tagging endogenous TFs using CRISPR/Cas9 genome editing technology (CETCh-seq). Here, we describe our general protocol of CETCh-seq for both adherent and nonadherent cell lines using a commercially available FLAG antibody.

Temporal Chunking Makes Life's Events More Memorable

Declines in episodic memory accompany both healthy aging and age-related diseases, such as dementia. Given that memory complaints are common in the aging population, a wealth of research has evaluated the underlying mechanisms of these declines and explored strategy interventions that could offset them. In the current paper, we describe a newer approach to improving memory: event segmentation training. Event segmentation is an encoding strategy in which individuals parse continuous activity into meaningful chunks. The ability to segment activity is associated with later memory for the events, but unfortunately, this segmentation ability declines with age. Importantly, interventions designed to improve event segmentation have resulted in memory improvements for both young and older adults. We will review these past experiments as well as some new event segmentation training work that uses older adults' semantic knowledge to improve their segmentation and episodic memory. We believe that future research on event segmentation is a promising avenue for improving older adults' ability to remember everyday activities.

Genomic regulation of invasion by STAT3 in triple negative breast cancer

Breast cancer is a heterogeneous disease comprised of four molecular subtypes defined by whether the tumor-originating cells are luminal or basal epithelial cells. Breast cancers arising from the luminal mammary duct often express estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth receptor 2 (HER2). Tumors expressing ER and/or PR are treated with anti-hormonal therapies, while tumors overexpressing HER2 are targeted with monoclonal antibodies. Immunohistochemical detection of ER, PR, and HER2 receptors/proteins is a critical step in breast cancer diagnosis and guided treatment. Breast tumors that do not express these proteins are known as "triple negative breast cancer" (TNBC) and are typically basal-like. TNBCs are the most aggressive subtype, with the highest mortality rates and no targeted therapy, so there is a pressing need to identify important TNBC tumor regulators. The signal transducer and activator of transcription 3 (STAT3) transcription factor has been previously implicated as a constitutively active oncogene in TNBC. However, its direct regulatory gene targets and tumorigenic properties have not been well characterized. By integrating RNA-seq and ChIP-seq data from 2 TNBC tumors and 5 cell lines, we discovered novel gene signatures directly regulated by STAT3 that were enriched for processes involving inflammation, immunity, and invasion in TNBC. Functional analysis revealed that STAT3 has a key role regulating invasion and metastasis, a characteristic often associated with TNBC. Our findings suggest therapies targeting STAT3 may be important for preventing TNBC metastasis.

CETCh-seq: CRISPR epitope tagging ChIP-seq of DNA-binding proteins

Chromatin immunoprecipitation followed by next-generation DNA sequencing (ChIP-seq) is a widely used technique for identifying transcription factor (TF) binding events throughout an entire genome. However, ChIP-seq is limited by the availability of suitable ChIP-seq grade antibodies, and the vast majority of commercially available antibodies fail to generate usable data sets. To ameliorate these technical obstacles, we present a robust methodological approach for performing ChIP-seq through epitope tagging of endogenous TFs. We used clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-based genome editing technology to develop CRISPR epitope tagging ChIP-seq (CETCh-seq) of DNA-binding proteins. We assessed the feasibility of CETCh-seq by tagging several DNA-binding proteins spanning a wide range of endogenous expression levels in the hepatocellular carcinoma cell line HepG2. Our data exhibit strong correlations between both replicate types as well as with standard ChIP-seq approaches that use TF antibodies. Notably, we also observed minimal changes to the cellular transcriptome and to the expression of the tagged TF. To examine the robustness of our technique, we further performed CETCh-seq in the breast adenocarcinoma cell line MCF7 as well as mouse embryonic stem cells and observed similarly high correlations. Collectively, these data highlight the applicability of CETCh-seq to accurately define the genome-wide binding profiles of DNA-binding proteins, allowing for a straightforward methodology to potentially assay the complete repertoire of TFs, including the large fraction for which ChIP-quality antibodies are not available.

Epizootics of sudden death in tammar wallabies (Macropus eugenii) associated with an orbivirus infection

Epizootics of sudden death in tammar wallabies (Macropus eugenii) occurred at six research facilities and zoological gardens in New South Wales, Australia, in late 1998 and at one Queensland research facility in March 1999. There were 120 confirmed tammar wallaby deaths during this period; however, population censuses indicated that up to 230 tammar wallabies may have died. The majority of animals died without premonitory signs. A small proportion of wallabies exhibited increased respiratory rate, sat with a lowered head shortly before death or were discovered in lateral recumbency, moribund and with muscle fasciculations. Gross postmortem findings consistently included massive pulmonary congestion, mottled hepatic parenchyma and subcutaneous oedema throughout the hindlimbs and inguinal region. Approximately 30% of the animals examined also had extensive haemorrhage within the fascial planes and skeletal muscle of the hindlimb adductors, inguinal region, ventral thorax, dorsal cervical region and perirenal retroperitoneal area. The tissues of affected animals became autolytic within a short period after death. Bacteriological examination of tissues from 14 animals did not provide any significant findings. Toxicological examination of the gastric and colonic contents of four animals did not reveal evidence of brodifacoume or other rodenticides. Viruses from the Eubenangee serogroup of the Orbivirus genus were isolated from the cerebral cortex of nine, and the myocardium of two, tammar wallabies and the liver and intestine of another tammar wallaby. A similar orbivirus was also isolated from the cerebrospinal fluid of another tammar wallaby that died suddenly. The disease agent appears to be a previously unrecognised orbivirus in the Eubenangee serogroup. This is the first report of epizootics of sudden deaths in tammar wallabies apparently associated with an orbivirus infection.

Role of CCCTC binding factor (CTCF) and cohesin in the generation of single-cell diversity of protocadherin-α gene expression

Extraordinary single-cell diversity is generated in the vertebrate nervous system by the combinatorial expression of the clustered protocadherin genes (Pcdhα, -β, and -γ). This diversity is generated by a combination of stochastic promoter choice and alternative pre-mRNA splicing. Here we show that both the insulator-binding protein CTCF and the cohesin complex subunit Rad21 bind to two highly conserved DNA sequences, the first within and the second downstream of transcriptionally active Pcdhα promoters. Both CTCF and Rad21 bind to these sites in vitro and in vivo, this binding directly correlates with alternative isoform expression, and knocking down CTCF expression reduces alternative isoform expression. Remarkably, a similarly spaced pair of CTCF/Rad21 binding sites was identified within a distant enhancer element (HS5-1), which is required for normal levels of alternative isoform expression. We also identify an additional, unique regulatory role for cohesin, as Rad21 binds to another enhancer (HS7) independently of CTCF, and knockdown of Rad21 reduces expression of the constitutive, biallelically expressed Pcdhα isoforms αc1 and αc2. We propose that CTCF and the cohesin complex initiate and maintain Pcdhα promoter choice by mediating interactions between Pcdhα promoters and enhancers.

Effects of sequence variation on differential allelic transcription factor occupancy and gene expression

A complex interplay between transcription factors (TFs) and the genome regulates transcription. However, connecting variation in genome sequence with variation in TF binding and gene expression is challenging due to environmental differences between individuals and cell types. To address this problem, we measured genome-wide differential allelic occupancy of 24 TFs and EP300 in a human lymphoblastoid cell line GM12878. Overall, 5% of human TF binding sites have an allelic imbalance in occupancy. At many sites, TFs clustered in TF-binding hubs on the same homolog in especially open chromatin. While genetic variation in core TF binding motifs generally resulted in large allelic differences in TF occupancy, most allelic differences in occupancy were subtle and associated with disruption of weak or noncanonical motifs. We also measured genome-wide differential allelic expression of genes with and without heterozygous exonic variants in the same cells. We found that genes with differential allelic expression were overall less expressed both in GM12878 cells and in unrelated human cell lines. Comparing TF occupancy with expression, we found strong association between allelic occupancy and expression within 100 bp of transcription start sites (TSSs), and weak association up to 100 kb from TSSs. Sites of differential allelic occupancy were significantly enriched for variants associated with disease, particularly autoimmune disease, suggesting that allelic differences in TF occupancy give functional insights into intergenic variants associated with disease. Our results have the potential to increase the power and interpretability of association studies by targeting functional intergenic variants in addition to protein coding sequences.

Cultured skin fibroblast cells derived from bluetongue virus-inoculated sheep and field-infected cattle are not a source of late and protracted recoverable virus

A recent hypothesis to explain the recurrence of bluetongue disease after winter seasonal absences of the vector has suggested a role for persistent infection of sheep. This report presents combined independent work from two laboratories investigating the possible recovery of Bluetongue virus (BTV) over a protracted period after infection of both sheep and cattle. Prior to infection with either cell-culture-adapted or non-culture-adapted BTV, sheep were subjected to a preliminary exposure to Culicoides sp. insects, which reportedly facilitates recovery of virus from infected sheep several months post-infection (p.i.). A series of skin biopsies at different intervals p.i. was used to establish skin fibroblast (SF) cultures from which attempts were made to detect virus by isolation and by molecular and immunological methods. Also examined was the effect on virus recovery of additional exposure to Culicoides sp. prior to skin biopsy during the post-inoculation period. A herd of cattle sentinels for surveillance of natural BTV infection in northern Australia was monitored prospectively for seroconversion. Evidence of infection initiated attempted virus recovery by establishing SF cultures. It was found that in both cattle and sheep there was not a protracted period over which BTV could be recovered from SF cultures. The data do not support a general hypothesis that BTV persists in either sheep or cattle.

Molecular diagnosis of lyssaviruses and sequence comparison of Australian bat lyssavirus samples

OBJECTIVE

To evaluate and implement molecular diagnostic tests for the detection of lyssaviruses in Australia.

DESIGN

A published hemi-nested reverse transcriptase polymerase chain reaction (RT-PCR) for the detection of all lyssavirus genotypes was modified to a fully nested RT-PCR format and compared with the original assay. TaqMan assays for the detection of Australian bat lyssavirus (ABLV) were compared with both the nested and hemi-nested RT-PCR assays. The sequences of RT-PCR products were determined to assess sequence variations of the target region (nucleocapsid gene) in samples of ABLV originating from different regions.

RESULTS

The nested RT-PCR assay was highly analytically specific, and at least as analytically sensitive as the hemi-nested assay. The TaqMan assays were highly analytically specific and more analytically sensitive than either RT-PCR assay, with a detection level of approximately 10 genome equivalents per microl. Sequence of the first 544 nucleotides of the nucleocapsid protein coding sequence was obtained from all samples of ABLV received at Australian Animal Health Laboratory during the study period.

CONCLUSION

The nested RT-PCR provided a means for molecular diagnosis of all tested genotypes of lyssavirus including classical rabies virus and Australian bat lyssavirus. The published TaqMan assay proved to be superior to the RT-PCR assays for the detection of ABLV in terms of analytical sensitivity. The TaqMan assay would also be faster and cross contamination is less likely. Nucleotide sequence analyses of samples of ABLV from a wide geographical range in Australia demonstrated the conserved nature of this region of the genome and therefore the suitability of this region for molecular diagnosis.

Pathogenesis studies with Australian bat lyssavirus in grey-headed flying foxes (Pteropus poliocephalus)

OBJECTIVE

To examine the susceptibility of the grey-headed flying fox (Pteropus poliocephalus) to Australian bat lyssavirus (ABL), and to provide preliminary observations on the pathogenesis of the disease in flying foxes.

PROCEDURE

Ten flying foxes were inoculated intramuscularly with ABL, and four with a bat-associated rabies virus. Inoculated animals were observed daily, and clinical samples collected every 9 to 14 days. Animals with abnormal clinical signs were euthanased, and samples collected for histological, serological, virological and immunohistological examinations. At 3 months post inoculation (PI), all survivors were euthanased, and each submitted to a similar examination.

RESULTS

Three ABL-inoculated flying foxes, and two rabies-inoculated animals developed abnormal clinical signs between 15 and 24 days PI. All three ABL-inoculated animals had histological lesions consistent with a lyssavirus infection, and lyssaviral antigen was identified in the central nervous system (CNS) of each. Virus was isolated from the brain of two affected animals. Of the rabies-inoculated flying foxes, both had histological lesions and viral antigen in the CNS. Virus was recovered from the brain of only one. None of the five affected flying foxes developed anti-lyssavirus antibodies, but, by 3 months PI, five of the seven ABL-inoculated survivors, and one of the two rabies virus-inoculated survivors, had seroconverted. The dynamics of the immune responses were quite variable.

CONCLUSIONS

The response of flying foxes to ABL, administered by a peripheral route of inoculation, was similar to that of bats inoculated peripherally with bat-derived rabies viruses.

Experimental infections of pigs with Japanese encephalitis virus and closely related Australian flaviviruses

The flavivirus Japanese encephalitis (JE) virus has recently emerged in the Australasian region. To investigate the involvement of infections with related enzootic flaviviruses, namely Murray Valley encephalitis (MVE) virus and Kunjin (KUN) virus, on immunity of pigs to JE virus and to provide a basis for interpretation of serologic data, experimental infections were conducted with combinations of these viruses. Antibody responses to primary and secondary infections were evaluated using panels of monoclonal antibody-based blocking enzyme-linked immunosorbent assays and microtiter serum neutralization tests (mSNTs). Identification of the primary infecting virus was possible only using the mSNTs. Following challenge, unequivocal diagnosis was impossible due to variation in immune responses between animals and broadened and/or anamnestic responses. Viremia for JE virus was readily detected in pigs following primary infection, but was not detected following prior exposure to MVE or KUN viruses. Boosted levels of existing cross-neutralizing antibodies to JE virus suggested a role for this response in suppressing JE viremia.

EHDV-1, a new Australian serotype of epizootic haemorrhagic disease virus isolated from sentinel cattle in the Northern Territory

In 1992, a virus (DPP2209) isolated from sentinel cattle located at Coastal Plains Research Station, latitude 12 degrees 39'S, longitude 131 degrees 20'E, approximately 60 km east of Darwin, Northern Territory. This virus was identified as a serotype of epizootic haemorrhagic disease (EHD) of deer virus previously undescribed in Australia. An additional 17 isolation of this virus were made from eight animals during the period February to May. Electron microscopic studies showed the presence of orbivirus-like structures. Serogrouping ELISA, indirect immunofluorescence assay and the serogrouping plaque reduction neutralisation test indicated the virus was a member of the epizootic haemorrhagic disease serogroup. Serotype specific plaque reduction neutralisation tests, indicated the virus was a member of the epizootic haemorrhagic disease serogroup not previously isolated in Australia. Analysis of the VP3 gene confirmed this observation. Cross neutralisation testing of the isolate with known epizootic haemorrhagic disease serotype viruses including endemic Australian and exotic strains identified isolate DPP2209 as epizootic haemorrhagic disease virus serotype 1.

Detection by ELISA of bluetongue antigen directly in the blood of experimentally infected sheep

An antigen-capture ELISA (Ag-ELISA) was developed to detect bluetongue virus (BTV) antigen directly from blood samples. Four blood preparations [whole blood, buffy coat, washed red blood cells (RBC) and plasma] taken pre-inoculation and on days 6 to 9 post-inoculation (PI) were used in the ELISA to study antigenaemia in forty sheep, each experimentally infected with one of 20 South African BTV serotypes. Seventeen of the 20 serotypes were detected and 27 of the 40 sheep were at some stage Ag-ELISA positive. Over the period of sampling, Ag-ELISA positive results were most frequently returned from whole blood taken on days 6 and 7 PI. However in some instances the quantity and/or duration of BTV antigenaemia was greater in buffy coat and washed RBC preparations. In a selection of samples examined, positive Ag-ELISA results were generally obtained when samples had an infectious virus titre in eggs of > 10(3.2) egg lethal doses (ELD50/ml). The appearance and duration of detectable antigenaemia was compared with the development of clinical signs and antibody responses of infected sheep. On days 6 and 7 PI the presence of fever (> 40 degrees C) was indicative to the likelihood of detectable antigenaemia. After day 5 PI antigenaemia declined and clinical signs of swollen face and inflamed feet appeared together with the first detectable antibody response. The Ag-ELISA, when used in conjunction with clinical observations and serologic data, should be useful as a rapid diagnostic procedure for bluetongue disease.

The use of an indirect ELISA with protein G-peroxidase conjugate and a blocking ELISA to demonstrate recent bluetongue infection in sheep

The humoral immune response of sheep infected with bluetongue virus serotypes 3, 9 and 16 was monitored by plaque inhibition (PI), blocking ELISA (BELISA) and indirect ELISA over a period of 63 days post-infection. Results indicated that testing of a single plasma or serum sample by both a BELISA and an indirect ELISA using a recombinant streptococcal protein G (PrG) peroxidase conjugate enabled an assessment of the proximity of a recent infection based on the failure of PrG to bind ovine IgM class antibodies. When BELISA and indirect ELISA results were expressed as a ratio, values indicative of recent infection (> or = 5) were observed for an average duration of 16.5 days (range 8 to 23 days) following the initial detection of antibody by BELISA. This approach has potential to improve diagnosis of a wide range of virus infections by providing an indicator for the relationship of serological status with a recent infection. However, where reinfection may occur, as with bluetongue virus, alternative methods may be required for definitive diagnosis.

Identification of epizootic haemorrhagic disease of deer virus serotypes using a fluorescence inhibition test

A fluorescence inhibition test (FIT) is described for serotyping rapidly isolates of epizootic haemorrhagic disease of deer virus (EHDV). The test used a serogroup-reactive monoclonal antibody in a immunofluorescence procedure to detect virus which resisted neutralisation by antisera to any of the eight known EHDV serotypes. The EHDV FIT provided an accurate serotype identification procedure for all eight reference serotypes and, in comparison with the plaque inhibition assay, abbreviated the serotyping process by three to four days.