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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. [ABSTRACT FROM AUTHOR]

To reduce the largemouth bass ulcer syndrome (LBUSV) aquatic economic losses, it must take effective preventive measures and coping strategies should be urgently investigated. In this research, the effects of a functionalized single-walled carbon nanotubes (SWCNTs) applied as a delivery vehicle for DNA vaccine administration in largemouth bass (Micropterus Salmoides) against LBUSV were studied. Our results showed that SWCNTs loaded with DNA vaccine induced a better protection to largemouth bass against LBUSV. We found more than 10 times increase in serum antibody levels, enzyme activities and immune-related genes (IL-6, IL-8, IFN-γ, IgM and TNF-α) expression, in the SWCNTs-pcDNA- MCP immunized groups compared with PBS group and the pure SWCNTs group. The survival rates for control group (PBS), pure SWCNTs groups (40 mg L−1), four pcDNA- MCP groups (5 mg L−1, 10 mg L−1, 20 mg L−1 and 40 mg L−1) and four SWCNTs-pcDNA- MCP groups (5 mg L−1, 10 mg L−1, 20 mg L−1 and 40 mg L−1) were 0%, 0%, 0%, 2.77%, 11.11%, 19.44%, 27.78%, 38.89%, 52.78% and 61.11%, respectively. Our results demonstrate that the SWCNTs-DNA vaccine can be used as a new method against LBUSV showing protection following challenge with LBUSV. • SWCNTs was used as an efficient DNA vaccine vector against LBUSV infection. • Immersed DNA vaccine confers strong immunity against LBUSV. • SWCNTs enhance the immunological effect of DNA vaccines. [ABSTRACT FROM AUTHOR]

Largemouth bass ulcerative syndrome virus (LBUSV) is an important virus induce the mortality of largemouth bass (Micropterus Salmoides). In this study, we reported a single-walled carbon nanotubes (SWCNTs) containing LBUSV major capsid protein (MCP) subunit vaccine (SWCNTs-MCP) which was evaluated for its protective effect on largemouth bass by immersion immunization. We found an elevation in serum antibody levels, enzyme activities, complement C3 content and immune-related genes (IgM, TGF-β, IL-1β, IL-8, TNF-α and CD4) expression, in the SWCNTs-MCP immunized groups compared with the pure MCP group. The survival rates for control group, pure MCP protein groups (40 mg L−1) and four SWCNTs-MCP groups (5 mg L−1, 10 mg L−1, 20 mg L−1 and 40 mg L−1) were 0%, 27.78%, 30.56%, 50.00%, 66.67% and 80.56%, respectively. The results suggests that with the assistance of SWCNTs, the immune protection of the SWCNTs-MCP group (40 mg L−1) increased up 52.78%–80.1% compared with pure MCP group (40 mg L−1). Our results demonstrate that the single-walled carbon nanotube subunit vaccine can be used as a new immunization method against LBUSV showing protection following challenge with LBUSV. Taken together, our results demonstrate that the single-walled carbon nanotube subunit vaccine can be used as a new method against LBUSV and have a high immune protection during the largemouth bass farm. • Largemouth bass immersed with SWCNTs-MCP confers strong immunity against LBUSV. • SWCNTs enhance the immunological effect of bath vaccines. • SWCNTs based immersion vaccine have prospects for application in aquatic vaccine. [ABSTRACT FROM AUTHOR]

Micropterus Salmoides rhabdovirus (MSRV), as a common aquatic animal virus, can cause lethal and epidemic diseases in the cultivation of largemouth bass. In this study, we reported a kind of immersion single-walled carbon nanotubes-loaded subunit vaccine which composited by glycoprotein (G) of MSRV, and evaluated its protective effect on largemouth bass. The results showed that a stronger immune response including serum antibody levels, enzyme activities (superoxide dismutase, acid phosphatase, alkaline phosphatase and total antioxidant capacity), complement C3 content and immune-related genes (IgM , TGF-β , IL-1β , IL-8 , TNF-α , CD4) expression can be induced obviously with single-walled carbon nanotubes-glycoprotein (SWCNTs-G) groups compared with G groups when largemouth bass were vaccinated. After bath immunization with G or SWCNTs-G for 28 days, fish were challenged with a lethal dose of MSRV. The survival rates for control group (PBS), SWCNTs group (40 mg L−1), pure G protein groups (40 mg L−1) and three SWCNTs-G groups (5 mg L−1, 10 mg L−1 and 40 mg L−1) were 0%, 0%, 39.5%, 36.7%, 43.6%and 70.1%, respectively. Importantly, with the assistance of SWCNTs, the immune protective rate of the SWCNTs-G group (40 mg L−1) increased by approximately 30.6%. This study suggested that SWCNTs-G is a promising immersion subunit vaccine candidate against the death caused by MSRV. • Largemouth bass immersed with SWCNTs-G confers strong immunity against MSRV. • SWCNTs as a promising vehicle can enhance immune effect of subunit vaccine. • SWCNTs based immersion vaccine have prospects for application in aquatic vaccine. [ABSTRACT FROM AUTHOR]