Elsevier

Available online 25 July 2020

Fish & Shellfish Immunology

Highlights

A DNA vaccine (pCDNA3.1(+)-MCP-flag) against largemouth bass virus (LMBV) based on the MCP gene was constructed.

Both innate and adaptive immune responses were induced in largemouth bass after vaccination with the pCDNA3.1(+)-MCP-flag DNA vaccine.

pCDNA3.1(+)-MCP-flag distributed in the head kidney, liver and spleen during vaccination.

RPS of largemouth bass vaccinated with DNA vaccine against LMBV was 63%.

pCDNA3.1(+)-MCP-flag can be used as a candidate DNA vaccine for the control of LMBV.

Abstract

Largemouth bass virus (LMBV) is the causative agent of a disease causing high mortality rates in largemouth bass during summer. However, there is little information available about the development of vaccines for LMBV disease. Hence, a DNA vaccine, named pCDNA3.1(+)-MCP-Flag, was constructed by inserting the cloned LMBV major capsid protein (MCP) gene into the pCDNA3.1(+)-Flag plasmid. The expression of the recombinant plasmid was confirmed by Western blot (WB) and RT-PCR. The WB result revealed that the MCP protein produced a band of approximately 53 kDa, consistent with the expected result. The RT-PCR results also confirmed that MCP was transcribed in the EPC cells transfected with the recombinant plasmid. The largemouth bass in the DNA vaccine group were immunized with the pCDNA3.1(+)-MCP-Flag plasmid by pectoral fin base injection, and the relative percent survival (RPS) of fish challenged with LMBV was 63%. The relative immunological analyses were as follows. Compared with the PBS and pCDNA3.1(+) groups, the DNA vaccine group showed significantly upregulated expression of IL-1β, IL-8, TNF-α and Mx in the spleen, head kidney and liver. All largemouth bass immunized with the DNA vaccine produced a high titre of LMBV-specific neutralizing antibody during the immunization period. The titre was 1:375 ± 40 and peaked at 14 days post-vaccination. The expression of the recombinant plasmid was analysed in the tissues of the DNA vaccine group by RT-PCR. The recombinant plasmid was expressed in the spleen, head kidney and liver, and MCP protein was successfully expressed after vaccination. In conclusion, the recombinant plasmid expressing LMBV MCP induced significant immune responses in largemouth bass, and might represent a potential LMBV vaccine candidate for largemouth bass.

Keywords

Largemouth bass virus

DNA vaccine

Major capsid protein

Protective immunity

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© 2020 Published by Elsevier Ltd.



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