Screening of horse polyclonal antibodies with a random peptide library displayed on phage: identification of ligands used as antigens in an ELISA test to detect the presence of antibodies to equine arteritis virus.

A random hexapeptide fusion-phage library was screened to isolate phages that bind to antibodies present in horse sera positive for equine arteritis virus (EAV). Analysis of the peptide sequences displayed by isolated phages identified seven groups. 25% of the isolated phages used as antigens in an ELISA test were specifically recognised by a pool of sera which was positive for EAV in virus neutralisation test (VN). Five of these, when used as antigen in ELISA, detected greater than 50% of sera (n = 30) containing antibodies to EAV as detected by VN. When these five phages were pooled together and used as antigen in ELISA, the detection was improved. The sensitivity and specificity of the ELISA were 99 and 71%, respectively, compared with the EAV neutralisation test (n = 200). This study has shown the potential that phage display libraries have for identifying peptide sequences which could be used as antigen in diagnostic ELISAs.