Trout sera titers are comparable to those found in salmonids vaccinated with DNA vaccines for rhabdovirus that varied depending on fish size, vaccine dose, time after vaccination, etc. [14] and [15]. Similar IPNV-seropositive percentage

was also observed, from 33 to 100% of fish, after vaccination of salmonids with laboratory MLN0128 research buy or commercial recombinant vaccines [8], [9] and [13]. Finally, we also evaluated the viral load after IPNV-challenge in controls and pIPNV-PP vaccinated trout by means of real-time PCR. We assayed the viral load in the head kidney at 7 days post-IPNV injection since this is one of the main replication targets for IPNV and at this time there is a peak in the detection of IPNV VP2 gene expression through PCR [32] and [39]. This approximation through means of reduction in viral load has been already assayed [8] and [23] and constitutes an approximation to field challenges, mainly for those challenges difficult to develop and analyse such as in the case of IPNV [12] and [13]. The viral load in pIPNV-PP vaccinated trout after IPNV injection, measured by IPNV VP1 gene transcripts, was 665-fold lower than Dabrafenib solubility dmso in fish injected with PBS alone. As observed before, the injection of the empty plasmid produced a little reduction of the viral

load, a 27-fold decrease of IPNV VP1 transcripts, when compared to the PBS controls. The same applied to a previous report from our group showing that the empty plasmid or the VHSV DNA vaccine decreased the viral load after VHSV challenge [23] although comparison between the two studies are difficult since the viral pathogenesis is different. In comparison, using a recombinant VP2 vaccine produced in yeast, the viral load was only decreased 22.4-fold when administered by intraperitoneal injection and 12.25-fold when delivered by immersion [8]. In conclusion, we have generated a DNA vaccine much consisting of a plasmid encoding the IPNV polyprotein (pIPNV-PP), based on the long

ORF of the segment A, which is properly translated as a polyprotein to be later processed through the active VP4-protease activity into preVP2, mature VP2 and VP3 proteins. Fish EPC cells transfected with this plasmid expressed the vaccine, which induced expression of Mx and showed structures resembling VLPs. Finally, rainbow trout vaccination with our plasmid regulated the expression of immune-relevant genes in a much lower extent compared to the rhabdoviral DNA vaccines, significantly induced neutralizing antibodies and was capable of decreasing the viral load after challenge. Even though further studies are necessary to demonstrate if this DNA vaccine is completely protective using good challenge models, our work provides a new effective fish DNA vaccine with a different mode of action compared to rhabdovirus DNA vaccines.