Glycoprotein (G protein)-based DNA vaccines are effective
in protecting aquaculture fish from rhabdoviruses but the degree
of immune response they elicit depends on plasmid concentration
and antigen cassette. Here, we developed a DNA
vaccine using the viral hemorrhagic septicemia virus G (VG)
gene and chemokine (C-C motif) ligand 19 (CCL19)a.2 regulated
by the CMV promoter as the molecular adjuvant. After
transfection of the prepared plasmid (pVG + CCL19) into epithelioma
papulosum cyprini cells, mRNA expression was confirmed
through quantitative real-time polymerase chain reaction.
The vaccine was intramuscularly injected into zebrafish
(Danio rerio), and 28 days after immunization, viral hemorrhagic
septicemia virus (105 TCID50/10 μl/fish) was intraperitoneally
injected. A survival rate of 68% was observed in the
pVG + CCL19 group but this was not significantly different
from the survival rate of fish treated with pVG alone, that is,
without the adjuvant. However, the expression of interferonand
cytokine-related genes in the spleen and kidney tissues
of zebrafish was significantly increased (p < 0.05) on days 1,
3, 7, and 14 after immunization. Thus, CCL19a.2 induced an
initial immune response as a molecular adjuvant, which may
provide initial protection against virus infection before vaccination-
induced antibody formation. This study provides insights
on the functions of CCL19a.2 adjuvant in DNA vaccines.
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