Although adaptive immunity is believed to exist only in higher vertebrates, recent studies showed the
ability to vaccinate shrimp and other crayfish against white spot syndrome virus (WSSV). This study
attempted to establish parameters of vaccination coordinated with subsequent viral challenge to gain
insights into the mechanisms of the protective response of penaeid shrimp. Two WSSV envelope proteins,
VP28 and VP36B, were used as subunit vaccines expressed in Escherichia coli followed by histidinetag
affinity chromatographic purification. Shrimp vaccinated with the recombinant WSSV proteins and
challenged with diluted WSSV inocula were intramuscularly injected in order to give a precise load.
Results of the viral challenge trials showed complete survival in the rVP28 group in contrast to the
rVP36B and PBS groups which exhibited 100% mortality. But this effective protection was exclusively
induced from a combination of a higher dosage of rVP28 and a lower viral challenge pressure. The innate
immune parameters analyzed among the three groups revealed that rVP28-treated shrimp showed the
highest activity level (p < 0.05) of phenoloxidase and superoxide dismutase during the entire period of
7 days post-vaccination. But there were no significant differences (p > 0.05) in mRNA abundances of the
Down syndrome cell adhesion molecule (Dscam) among all groups. In addition, total hemocyte counts
significantly decreased in shrimp treated with the recombinant viral proteins compared to the PBS group.
These results indicated that the existence of structure- and dose-dependent protective responses and
the elevated innate immunity in shrimp following a protein-based vaccination might be responsible for
conferring resistance against WSSV.
© 2012 Elsevier B.V. All rights reserved.