| Vaccination is an important measure to prevent and control the spread of highly pathogenic avianinfluenza (HPAI). Recombinant vaccine master seed virus created by reverse genetics can providecomplete protection for chickens in China. However, the existing oil-emulsion inactivated vaccines stillsuffered from some drawbacks, including typically slow antibody response, low antibody titers inbroilers. Therefore, it is urgent to further improve efficacy of the existing inactivated vaccines.Staphylococcal enterotoxins A (SEA) characterized by superantigen activity has the potential to improvethe immunogenicity of inactivated antigen, which makes it become an idea adjuvant candidate.This study constructed a prokaryotic expressed plasmid pET-SEA which was induced to expresssoluble recombinant SEA (rSEA) under the optimal condition. Bioactivity identification indicated rSEAstimulated the potent proliferation of chicken PBMC, suggesting rSEA possessed high bioactivity. Toevaluate the effect of rSEA on efficacy of inactivated vaccine, the study emulsified AIV inactivatedvaccines derived from a novel vaccine strain Re-6containing several levels of rSEA, such as super-high(400μg/0.3mL), high (100μg/0.3mL), medium (10μg/0.3mL), low (1μg/0.3mL), minimum(0.1μg/0.3mL) and rSEA-free inactivated vaccine. In addition, the study also emulsified NDVinactivated vaccines derived from the NDV LaSota strain containing several levels rSEA, such as high(100μg/0.3mL), medium (10μg/0.3mL) and rSEA-free inactivated vaccine.Test results in SPF chickens indicated that, at days7post-vaccination, the average HI antibodytiters and the value of CD4+/CD8+of all chickens that immunized with AIV vaccines containing rSEAwere always much higher than rSEA-free immunized group(p<0.05). The average HI antibody titers inthe medium level of rSEA group and in rSEA-free group were3.3log2and0, respectively. Thechallenge at7days post-vaccination showed that4/8of chickens in the medium level of rSEA groupshed the challenge viruses, whereas all chickens(8/8) in the rSEA-free immunized group shed viruses.The other challenge at10-day post-vaccination showed that chickens in the medium level of rSEAgroup remained healthy during the2-week observation period and the challenge virus was no detectedfrom their swabs, whereas the challenge viruses were recovered from3/8of chickens in the rSEA-freegroup despite none of the chickens died. The average antibody titers in all groups immunized withvaccines containing rSEA were no less than10log2, which are significant difference compared with8.8log2in the rSEA-free group at days21post-vaccination(p<0.05). All samples including muscles andorgans collected from rSEA-adjuvanted groups to detect rSEA residual are negative at28dayspost-vaccination. The study indicated that the inactivated vaccine containing rSEA is capable ofeliciting higher immune response and more rapid immune protection than rSEA-free vaccine.Test results in broilers showed, the average HI antibody titers reached5.6log2in the groupimmunized with vaccine containing high level of rSEA and4.2log2in the group immunized withvaccine containing medium level of rSEA at14-day post-vaccination, which was more significant than2.9log2of rSEA-free immunized group (p<0.01). The average HI antibody titers reached the peak of8.5log2and8.0log2in the group immunized with vaccine containing high level of rSEA and medium level of rSEA at28-day post-vaccination, respectively, which were more significant than6.8log2ofrSEA-free immunized group (p<0.01). More importantly, the average HI antibody titers and peaks inboth rSEA-adjuvanted immunized groups were significant difference compared with the rSEA-freegroup during the initial period of4-week (p<0.05). The T lymphocyte subpopulation assay showed thatthe CD4+and CD4+/CD8+value in high level of rSEA immunized group were higher than that ofrSEA-free group (p<0.05). This study indicated that rSEA can induce broiler to generate high humoralimmunity and cellular immune response.The HI antibody titers of chickens immunized with NDV inactivated vaccine containing rSEAwere greater than those of rSEA-free immunized group（p<0.05）. The average HI antibody titers in highlevel of rSEA group were4.2log2, which was more significant than1.7log2of rSEA-free immunizedgroup (p<0.01). This study showed rSEA can also enhance efficacy of NDV inactivated vaccine.In conclusion, rSEA can not only contribute to the velocity and enhancement of humoral immunityinduced by immune antigens, but also elicit cell-mediated immune response, thereby improve the abilityof unprimed subjects against disease. Therefore, rSEA can improve efficacy of inactivated vaccine, andis a safe immunoenhancer. |
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