Detection of antibodies against equine herpesvirus types 1 and 4 by using recombinant protein derived from an immunodominant region of glycoprotein B

Intranasal IgG4/7 antibody responses protect horses against equid herpesvirus-1 (EHV-1) infection including nasal virus shedding and cell-associated viremia

Equid herpesvirus-1 (EHV-1) outbreaks continue despite widely used vaccination. We demonstrated previously that an ORF1/ORF71 gene deletion mutant of the EHV-1 strain Ab4 (Ab4ΔORF1/71) is less virulent than its parent Ab4 virus. Here, we describe the Ab4 challenge infection evaluating protection induced by the Ab4ΔORF1/71 vaccine candidate. Susceptible control horses developed respiratory disease, fever, nasal shedding, and viremia. Full protection after challenge infection was observed in 5/5 previously Ab4 infected horses and 3/5 Ab4ΔORF1/71 horses. Two Ab4ΔORF1/71 horses developed short-lasting viremia and/or virus shedding. Protective immunity in the respiratory tract was characterized by pre-existing EHV-1-specific IgG4/7 antibodies, the absence of IFN-α secretion and rapidly increasing IgG4/7 upon challenge infection. Pre-existing systemic EHV-1-specific IgG4/7 highly correlated with protection. T-cell immunity was overall low. In conclusion, protective immunity against EHV-1 infection including prevention of viremia was associated with robust systemic and intranasal IgG4/7 antibodies suggesting immediate virus neutralization at the local site.

Recombinant protein-based viral disease diagnostics in veterinary medicine

Identification of pathogens or antibody response to pathogens in human and animals modulates the treatment strategies for naive population and subsequent infections. Diseases can be controlled and even eradicated based on the epidemiology and effective prophylaxis, which often depends on development of efficient diagnostics. In addition, combating newly emerging diseases in human as well as animal healthcare is challenging and is dependent on developing safe and efficient diagnostics. Detection of antibodies directed against specific antigens has been the method of choice for documenting prior infection. Other than zoonosis, development of inexpensive vaccines and diagnostics is a unique problem in animal healthcare. The advent of recombinant DNA technology and its application in the biotechnology industry has revolutionized animal healthcare. The use of recombinant DNA technology in animal disease diagnosis has improved the rapidity, specificity and sensitivity of various diagnostic assays. This is because of the absence of host cellular proteins in the recombinant derived antigen preparations that dramatically decrease the rate of false-positive reactions. Various recombinant products are used for disease diagnosis in veterinary medicine and this article discusses recombinant-based viral disease diagnostics currently used for detection of pathogens in livestock and poultry.

Utilisation of bacteriophage display libraries to identify peptide sequences recognised by equine herpesvirus type 1 specific equine sera

Three filamentous phage random peptide display libraries were used in biopanning experiments with purified IgG from the serum of a gnotobiotic foal infected with equine herpesvirus-1 (EHV-1) to enrich for epitopes binding to anti-EHV-1 antibodies. The sequences of the amino acids displayed were aligned with protein sequences of EHV-1, thereby identifying a number of potential antibody binding regions. Presumptive epitopes were identified within the proteins encoded by genes 7 (DNA helicase/primase complex protein), 11 (tegument protein), 16 (glycoprotein C), 41 (integral membrane protein), 70 (glycoprotein G), 71 (envelope glycoprotein gp300), and 74 (glycoprotein E). Two groups of sequences, which aligned with either glycoprotein C (gC) or glycoprotein E (gE), identified type-specific epitopes which could be used to distinguish between sera from horses infected with either EHV-1 or EHV-4 in an ELISA using either the phage displaying the peptide or synthetic peptides as antigen. The gC epitope had been previously identified as an immunogenic region by conventional monoclonal antibody screening whereas the gE antibody binding region had not been previously identified. This demonstrates that screening of phage display peptide libraries with post-infection polyclonal sera is a suitable method for identifying diagnostic antigens for viral infections such as EHV-1.

Development and validation of a monoclonal antibody blocking ELISA for the detection of antibodies against both equine herpesvirus type 1 (EHV1) and equine herpesvirus type 4 (EHV4)

A monoclonal antibody blocking ELISA was developed for the detection of antibodies directed against either EHV1 or EHV4. For this purpose, we selected a monoclonal antibody directed against a cross-reactive, conservative and immunodominant epitope of both EHV1 and EHV4. High antibody titres were found in rabbit antisera and SPF-foal antisera infected with either EHV1 or EHV4. After experimental challenge of conventional horses with EHV1 or EHV4 significant increases in CF and ELISA titres were found, whereas VN antibodies did not always increase significantly. In 344 paired serum samples submitted for diagnostic purposes a good agreement (kappa = 0.75, confidence limits = 0.63-0.88) was found between VN test and ELISA regarding a significant increase in titres. Also, a good correlation was found between VN and ELISA titres (r = 0.76, p<<0.0005). The relative sensitivity and specificity of the Mab blocking ELISA as compared with the VN test were 99.9 and 71%, respectively. The rather low relative specificity of the ELISA may be explained by a relatively low sensitivity of the VN test. The ELISA also detected increases in titre after vaccination with an EHV1 subunit vaccine, and after primary field infections in weaned foals. We concluded that the Mab blocking ELISA is more sensitive, easier to perform, more rapid and more reproducible than the VN test. We consider this test as a valuable tool for serological diagnosis of both EHV1 and EHV4 infections.

Recombinant rubella E1 fusion proteins for antibody screening and diagnosis

BACKGROUND

Until rubella is eradicated there will be a continuing need for rubella antibody surveillance. Antigen production using recombinant DNA technology may be a viable alternative to traditional techniques of producing antigens for enzyme immunoassays (EIAs).

OBJECTIVES

To investigate the potential of bacterial fusion proteins containing rubella E1 protein sequences for use in EIAs to detect rubella antibodies.

STUDY DESIGN

Purified bacterial fusion proteins containing rubella E1 sequences to be used as antigens in EIAs and compared to 'traditional' assays using virus derived antigens for rubella antibody screening.

RESULTS

cDNA clones coding for the complete rubella E1 protein sequence and subfragments of E1 were modified for expression as carboxy terminal fusions with either beta-galactosidase or glutathione-S-transferase. beta-galactosidase fusions with the complete E1 coding sequence or amino acids 201 to 307, which contain known epitopes, resulted in the production of predominantly insoluble fusion proteins unsuitable for use in EIA. Nine glutathione-S-transferase-E1 fusion proteins were produced with individual fusion proteins exhibiting varying properties with regard to the levels of protein produced, apparent stability, solubility and the potential for affinity purification using glutathione agarose. Reduction of the E1 component to only 44 amino acids containing three B-cell epitopes (Terry et al., 1988) produced an abundant soluble GST-E1 fusion protein (3.5 mug/ml), which could be affinity purified using glutathione agarose. This fusion protein has been successfully used in EIA to detect rubella antibodies.

CONCLUSIONS

We have shown that GST-E1 fusions have potential as antigens in tests for rubella antibodies.