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

Development of a peptide ELISA for discrimination between serological responses to equine herpesvirus type 1 and 4

A peptide-based enzyme-linked immunosorbent assay (ELISA) for discrimination between serological responses to equine herpesvirus type 1 (EHV-1) and 4 (EHV-4) was developed. Three and four peptides for EHV-1 and EHV-4, respectively, were designed and studied initially in the ELISA using sera from foals infected experimentally. The most promising peptide pair, derived from EHV-1 glycoprotein E and EHV-4 glycoprotein G, was evaluated further using acute and convalescent sera from horses infected experimentally and naturally as well as a panel of horse field sera. Ten pre- and post-vaccination serum pairs were similarly tested in the type-specific ELISA. The peptide ELISA was able to identify horses which had been infected with EHV-1 or EHV-4 as derived from the results using acute and convalescent sera collected from natural outbreaks. When applied to a set of field samples, the assay proved robust with respect to determining the EHV-1 and EHV-4 antibody status. Also, the peptide ELISA was able to detect type-specific seroconversion for EHV-1 in vaccinated animals. With further validation, the EHV-1/EHV-4 peptide ELISA described in this study could serve as a reliable and cost-effective alternative to current methods for serological EHV-1 and EHV-4 diagnosis.

Purification of polyclonal anti-conformational antibodies for use in affinity selection from random peptide phage display libraries: a study using the hydatid vaccine EG95

The use of polyclonal antibodies to screen random peptide phage display libraries often results in the recognition of a large number of peptides that mimic linear epitopes on various proteins. There appears to be a bias in the use of this technology toward the selection of peptides that mimic linear epitopes. In many circumstances the correct folding of a protein immunogen is required for conferring protection. The use of random peptide phage display libraries to identify peptide mimics of conformational epitopes in these cases requires a strategy for overcoming this bias. Conformational epitopes on the hydatid vaccine EG95 have been shown to result in protective immunity in sheep, whereas linear epitopes are not protective. In this paper we describe a strategy that results in the purification of polyclonal antibodies directed against conformational epitopes while eliminating antibodies directed against linear epitopes. These affinity purified antibodies were then used to select a peptide from a random peptide phage display library that has the capacity to mimic conformational epitopes on EG95. This peptide was subsequently used to affinity purify monospecific antibodies against EG95.

Identification of peptides specific for antibodies in vitiligo using a phage library

Patients with vitiligo produce specific autoantibodies that can be detected in their sera. These antibodies are believed to play a role in the pathogenesis of this disease. A random peptide library displayed on phage is a technique that can be used to identify the epitopes that react with monoclonal and polyclonal antibodies. We used this technique to identify the epitopes that react specifically with the vitiligo autoantibodies. By screening the random peptide phage library and using ELISA, two clones that showed a higher frequency of reactivity with the antibodies in the sera of patients with vitiligo were identified. The peptides do not show any similarity with the autoantigens so far implicated in vitiligo, indicating that these epitopes may mimic conformational epitopes in proteins.

Identification of epitopes in the nucleocapsid protein of Nipah virus using a linear phage-displayed random peptide library

A random peptide library of heptamers displayed on the surface of M13 bacteriophage was used to identify specific epitopes of antibodies in pooled sera of swine naturally infected by Nipah virus. The selected heptapeptides were aligned with protein sequences of Nipah virus and several putative epitopes were identified within the nucleocapsid protein. A total of 41 of 60 (68%) selected phage clones had inserts resembling a region with the sequence SNRTQGE, located at the C-terminal end (amino acids 503-509) of the nucleocapsid protein. The binding of antibodies in the swine and human antisera to the phage clone was inhibited by a synthetic peptide corresponding to this region. Epitopes identified by phage display are consistent with the predicted antigenic sites for the Nipah virus nucleocapsid protein. The selected phage clone used as a coating antigen discriminated swine and human Nipah virus sera-positive from sera-negative samples exhibiting characteristics, which might be attractive for diagnostic tests.

Identification of equine herpesvirus-1 antigens recognized by cytotoxic T lymphocytes

Equine herpesvirus-1 (EHV-1) causes serious disease in horses throughout the world, despite the frequent use of vaccines. CTLs are thought to be critical for protection from primary and reactivating latent EHV-1 infections. However, the antigen-specificity of EHV-1-specific CTLs is unknown. The aim of this study was to identify EHV-1 genes that encode proteins containing CTL epitopes and to determine their MHC I (or ELA-A in the horse) restriction. Equine dendritic cells, transfected with a series of EHV-1 genes, were used to stimulate autologous CTL precursor populations derived from previously infected horses. Cytotoxicity was subsequently measured against EHV-1-infected PWM lymphoblast targets. Dendritic cells were infected with EHV-1 (positive control) or transfected with plasmids encoding the gB, gC, gD, gE, gH, gI, gL, immediate-early (IE) or early protein of EHV-1 using the PowderJect XR-1 research device. Dendritic cells transfected with the IE gene induced CTL responses in four of six ponies. All four of these ponies shared a common ELA-A3.1 haplotype. Dendritic cells transfected with gC, gD, gI and gL glycoproteins induced CTLs in individual ponies. The cytotoxic activity was ELA-A-restricted, as heterologous targets from ELA-A mismatched ponies were not killed and an MHC I blocking antibody reduced EHV-1-specific killing. This is the first identification of an EHV-1 protein containing ELA-A-restricted CTL epitopes. This assay can now be used to study CTL specificity for EHV-1 proteins in horses with a broad range of ELA-A haplotypes, with the goal of developing a multi-epitope EHV-1 vaccine.

Growth of recombinant equine herpesvirus 1 (EHV-1) replaced with passage-induced mutant gene 1 and gene 71 derived from an attenuated EHV-1 in cell cultures and in the lungs of mice

The relationship of passage-induced mutant genes 1 and 71 of an attenuated equine herpesvirus 1 (EHV-1) with virulence was analysed by constructing nine recombinant EHV-1 viruses by homologous recombination. Gene 1 or/and gene 71 of a virulent EHV-1 strain, HH1, was replaced by a mutant gene 1 or/and 71 of an attenuated HH1 strain, BK343, respectively. The beta-galactosidase gene of Escherichia coli was inserted within the gene 1 or 71 coding sequence of HH1 to inactivate the genes. Virus replications of these recombinant viruses in cell cultures were similar, but release of the gene 71-inactivated virus from infected cells was delayed compared to that of the other viruses. Plaque sizes of the recombinant viruses were similar to those of HH1, but those of BK343 were significantly smaller, indicating an effect of some unknown factor(s) on viral cell-to-cell spread. The growth abilities of the recombinant viruses with a mutant gene 1 or/and 71 in lungs of mice were similar to those of HH1, but those of gene 71-inactivated viruses were reduced to the level of BK343 and the titers were about 100-times lower than those of the other recombinant viruses. These results indicate that the mutant genes 1 and 71 of BK343 might not confer an attenuated nature to EHV-1.

Selection of phage-display library peptides recognizing ethanol targets on proteins

There is a forthcoming link between chronic alcohol consumption and proteins covalently modified by ethanol metabolites and their antibodies. To identify sensitive probes of protein-ethanol conjugates, we screened for the ethanol-altered protein domains with a phage-display combinatorial peptide library. In principle, recognition of the epitopes by the library peptides occurs through protein-protein interactions. A general screening, M13-based library with 10(9) random sequences of linear heptameric peptides was used. The peptides were displayed in five copies each, as fusion proteins with phage's minor coat protein III. They were located on one end of the surface of the phage particles. The targets were a model protein, streptavidin, and protein-ethanol conjugates (hydroxyethyl radical- or acetaldehyde-modified bovine serum albumin). They were either immobilized on a surface by direct coating or affinity captured on floating beads. An enriched library of phages with the tightest peptide binders for each target was selected and amplified in a multiple-cycle biopanning in vitro procedure. Binders were characterized by DNA sequencing of the corresponding phages and by counter-screening with positive and negative targets in either an enzyme-linked immunosorbent assay or plaque assay. We obtained the HPQ motif for streptavidin and two unique subsets of peptides that recognized each ethanol target with a selectivity of two orders of magnitude above the carrier protein and controls. The application of biopanning processes, coupled with phage-display peptide libraries on biological fluids and tissues, could provide a systematic mapping of protein--ethanol conjugates and supply a means for early diagnosis and prognosis of chronic alcohol consumption in human beings.