Screening of the dominant immunogenic epitopes of tilapia lake virus

Abstract

Tilapia lake virus (TiLV) is an emerged contagious pathogen resulting in high mortality and significant socio-economic impacts. Vaccination is the most effective way to protect fish against viral infections, and confirmation of immunogenic epitopes of virus is a prerequisite for designing vaccines. However, the immunogenic epitope of TiLV is unclear. In the study, the immunogenicity of all proteins encoded by TiLV genomic segments was evaluated to screen the dominant immunogenic epitope. All proteins (S1, S2, S3, S4, S527–172, S5196–272, S630–317, S7, S8, S9 and S10) encoded by TiLV genomic segments were obtained by gene cloning, vector construction, expression and purification. Healthy tilapia were vaccinated with these purified proteins, and the immunoprotective effects were evaluated. Results showed that the numbers of erythrocytes, leucocytes, lymphocytes and neutrophils increased significantly in S630–317, S8 and S10 vaccinated groups. The enzyme activities of T-AOC, SOD, ACP and AKP also showed higher levels in S630–317, S8 and S10 vaccinated groups. Additionally, the expression levels of immune-related genes (CC2, TNF-γ, IL-1β, CD4, MyD88 and IFN-γ) also significantly upregulated in S630–317, S8 and S10 vaccinated groups. The relative percentage survival (RPS) of tilapia vaccinated with S630–317, S8 and S10 reached 64.28%, 68.75% and 53.57% at 14 days post TiLV-infection, while the control groups had a 96% mortality rate. These results indicated that S630–317, S8 and S10 can induce strong immune responses. S8 is the dominant immunogenic epitope of TiLV, which can be the potential vaccine candidate for TiLV prevention and control.