Neutralizing scFv Antibodies against Infectious Bursal Disease Virus Isolated From a Nlpa-Based Bacterial Display Library

Abstract

Infectious bursal disease (IBD) considered as one of the major viral diseases threatening the poultry industry worldwide. The causative agent of the IBD is Infectious bursal disease virus (IBDV) which replicates in developing B lymphocytes in the bursa of Fabricius leading to its destruction and bursal inflammation. In this study, we investigated a technology to produce therapeutic recombinant antibodies against IBDV in bacteria by constructing a bacterial displayed recombinant scFv library from immunized chickens, followed by screening the scFv library by fluorescence activated cell sorting (FACS) with FITC-labeled VP2. Twelve VP2-binding scFv clones with unique sequences were obtained, with overall amino acid homology of 81.53%. The complementarity determining region (CDR) 3 in the heavy chain displayed the lowest homology, while the amino acid sequences in framework regions and CDR2 of both chains and CDR1 of the heavy chain are relatively conserved. Twelve VP2-binding scFv clones were expressed in E.coli and purified through denaturation and denaturation of inclusion bodies. Our ELISA results showed that all scFvs exhibited binding ability and specificity to VP2 and various IBDV strains. In addition, two scFvs showed significant neutralizing activity to IBDV (B-87 strain) as these scFvs inhibited cytopathic effect of chicken embryo fibroblast (DF1) caused by IBDV. In conclusion, our study provides a lead candidate for further development of therapeutic antibodies for IBDV infection.