Utilization of phage display to identify antigenic regions in the PCV2 capsid protein for the evaluation of serological responses in mice and pigs

Alternative use of phage display: phage M13 can remain viable in the intestines of poultry without causing damage

Phage display (PD) is a tool for developing new molecules to control pathogens. Peptides selected by PD are commonly synthesised and tested, but the use of phage M13 displaying the selected peptides as a direct biding in the intestinal tract has not yet been tested. This study evaluated whether phage M13 can remain viable in the chicken gastrointestinal tract and whether it causes injury or humoral immune response. We inoculated phage M13 or E. coli ER2738 (ECR) infected with M13 into birds at different ages. We found the virus in faeces at 5 or 13 days after inoculation, just when it infected the ECR. The presence of phage M13 or ECR did not result in gut injuries and had no impacts on weight gain and bird health. Furthermore, the levels of IgY were similar in all treatments, which indicates that the virus can be used in chicken until 42 days without being recognised by the immune system. This work provides a scientific basis for the use of PD as a tool in numerous applications to control different pathogens.

Phage M13 remains viable in the bird's intestine if inoculated with E. coli ER2738.

Bacteriophage M13 does not damage the chicken gut.

Phage M13 remains in the gut without leading to a humoral response up to 42 days.

Selection and Characterization of a Single-Chain Variable Fragment against Porcine Circovirus Type 2 Capsid and Impedimetric Immunosensor Development

Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus-associated disease (PCVAD) that causes huge global economic losses for the swine industry. Effective strategies or rapid detection of PCV2 in pig are essential to control PCVAD. Here, single-chain variable fragments (scFvs) were selected and characterized against the PCV2 capsid using phage display technology. Phage scFv clones were selected from the human scFv phagemid library (Tomlinson I + J) for direct panning against the PCV2 capsid. Eighty-four monoclonal phage scFvs were individually tested for binding to the PCV2 capsid by ELISA. Eight scFv clones showed significant binding to the PCV2 capsid and only three clones (clone nos. 13, 37, and 81) contained both VHCDRs and VLCDRs in the sequence. Clone scFv no. 81 had the highest reactivity to the PCV2 capsid and was constructed in the pET22b (+) expression vector. The recombinant was transformed to Escherichia coli BL21(DE3) for expression and purification. The scFv showed appropriate affinity to the PCV2 capsid by western blot analysis. Kinetics of scFv and the PCV2 capsid were determined using surface plasmon resonance and showed binding affinity in the nanomolar range (K D = 57.2 nM). Our scFv was first applied in the development of an impedimetric immunosensor for PCV2 capsid detection, and results showed that impedance increased with increasing PCV2 capsid expression with limit of detection = 114 nM. Findings demonstrated that our scFv has potential for use as a receptor for biosensor devices.