Antigenic epitope screening and functional modification of mannose enhance the efficacy of largemouth bass virus subunit vaccines

Abstract

Major capsid protein (MCP) can be used as a subunit vaccine against largemouth bass virus (LMBV). However, subunit vaccines usually have low immunogenicity. Here, to identify the major immunogenicity determinant region of the MCP gene, we truncated the MCP of the LMBV gene into four parts (MCP‐1, MCP‐2, MCP‐3 and MCP‐4). Enzyme‐linked immunosorbent assay (ELISA) was used to identify the antigenicity of these four truncated MCP proteins. Then, the highly antigenic truncated protein was modified with mannose and connected with functionalized single‐walled carbon nanotubes (SWCNTs) as carriers. Largemouth basses were immunized by bath immersion, challenged with LMBV on the 28th day after immunization and evaluated for related immune indicators. The results indicated that the MCP‐2 protein could induce a higher antibody titre than the other truncated MCP proteins. We found that the levels of immune‐related genes (TNF‐α, CD40, IgM, IFNγ and IL‐10) in the spleen and kidney were significantly increased in the MCP‐2 and MCP‐2‐Man groups. ELISA results showed that the antibody content in the serum increased significantly in the MCP‐2 group 7 days post‐vaccination and increased with days in all the vaccinated groups, with the highest observed on the 21st day. Notably, the MCP‐2‐Man vaccine (10 mg L−1) showed durability of immunoprotection efficacy that could protect largemouth basses from LMBV challenge, and the immune protection rate reached 78.94%. These results suggest that MCP‐2 might be the major immunogenicity determinant region of LMBV and that the mannose‐modified MCP‐2 vaccine can induce stronger adaptive immune responses.

Isolation, identification, and monoclonal antibody development of largemouth bass virus

“…Vaccination is considered an ideal approach for preventing LMBV infection. Although some candidate vaccines and herbal extracts have been proven to be potent for defending against LMBV infection under laboratory conditions, there is no licensed vaccine or antiviral drug available for preventing or treating LMBV infection (Jia et al, 2022;Yao et al, 2022;Cheng et al, 2023;Wang et al, 2023;Zhang, M. et al, 2023). Therefore, rapid detection and early diagnosis of LMBV remain crucial strategies to prevent the disease's spread and mitigate economic loss.…”

“…The selection of targets and the production of antibodies are two crucial aspects in the development of immunoassay strips as they directly influence their specificity and sensitivity (Li et al, 2021;Shen et al, 2021). The MCP, which is the most abundant structural protein carrying virus-specific antigens, has emerged as an ideal target for genetic relationship identification, vaccine research, antibody production, development of detection methods, and systematic survey (Montelongo-Alfaro et al, 2019;Guo et al, 2022;Jia et al, 2022;Yao et al, 2022;Qin et al, 2023;Zhang, M. et al, 2023). Thus, we developed the monoclonal antibodies against MCP and assessed their specificity, providing valuable material for the development of immunoassay strips for LMBV detection.…”