Dose effects of a DNA vaccine encoding immobilization antigen on immune response of channel catfish against Ichthyophthirius multifiliis.

Abstract Channel catfish (Ictalurus punctatus) vaccinated with pcDNA3.1-IAg52b plasmid DNA vaccine encoding immobilization antigen genes of Ichthyophthirius multifiliis (Ich) produced anti-Ich antibodies and were partially protected (20% survival) in a previous study. Here we evaluated whether a higher dose or two doses of pcDNA3.1-IAg52b vaccine could provide better protection for catfish against Ich. Fish were distributed into 6 groups and vaccinated using following schemes: 1.10 μg pcDNA3.1-IAg52b fish−1, 2.20 μg pcDNA3.1-IAg52b fish−1, 3. two doses of 10 μg pcDNA3.1-IAg52b fish−1 with 7 days between doses, 4.20 μg pcDNA3.1 fish−1 (mock-vaccinated control), 5.15,000 live theronts fish−1 (positive control), and 6. non-vaccinated and non-challenge control. Parasite infection levels, serum anti-Ich antibody levels, fish mortality and immune-related gene expression were determined during the trial. Fish vaccinated with a single dose of 20 μg pcDNA3.1-IAg52b fish−1 or two doses of 10 μg fish−1 had higher anti-Ich antibody levels than fish receiving a single dose of 10 μg fish−1. Survival was significantly higher in fish receiving 20 μg vaccine fish−1 (35.6%) or 2 doses of 10 μg fish−1 (48.9%) than fish injected with a single dose of 10 μg fish−1 (15.6%) or mock-vaccinated control (0%). Fish vaccinated at the dose 20 μg fish−1 had higher expression of vaccine DNA in muscle than fish vaccinated with 10 μg fish−1. Fish vaccinated with the DNA vaccine showed higher up-regulation than mock-vaccinated control in the expression of IgM, CD4, MHC I and TcR-α genes during most of time points after vaccination. Further studies are needed to improve efficacy of DNA vaccines by using multiple antigens in the DNA vaccines.