Primary immunization using low antigen dosages and immunological tolerance in rainbow trout

Area of Science:

• Aquatic animal health
• Immunology
• Fish vaccination

Background:

• Enteric redmouth disease (ERM), caused by Yersinia ruckeri, impacts salmonid farming.
• Vaccination offers protection, but efficacy varies with administration route.
• Oral vaccination studies suggest low antigen doses might induce immunological tolerance.

Purpose of the Study:

• To investigate if prolonged exposure to low Yersinia ruckeri antigen doses induces susceptibility to ERM in rainbow trout.
• To evaluate the impact of different vaccine dosages and administration routes (bath, feed) on rainbow trout immune response and protection against ERM.

Main Methods:

• Rainbow trout were immunized via immersion or feed with varying Yersinia ruckeri antigen dosages.
• Fish were subsequently challenged with live Yersinia ruckeri.
• Survival rates were recorded, and immune responses were analyzed using ELISA and qPCR, focusing on regulatory T cell markers.

Main Results:

• Sub-optimal immunization with low antigen doses (bath or feed) did not protect against Yersinia ruckeri challenge and sometimes resulted in lower survival than controls.
• Fish receiving high antigen doses showed down-regulation of immune-suppressive cytokines and FoxP3, indicating reduced regulatory T cell activity compared to low-dose groups.
• Repeated exposure to low antigen concentrations appeared to induce immune tolerance in rainbow trout.

Conclusions:

• Repeated, low-dose Yersinia ruckeri antigen exposure can induce immune tolerance in rainbow trout.
• Sub-optimal vaccination strategies may compromise fish health and increase susceptibility to ERM.
• High antigen dosages are recommended for primary immunization to ensure effective protection against enteric redmouth disease in trout.