Transcriptome analysis of plasmid-induced genes sheds light on the role of type I IFN as adjuvant in DNA vaccine against infectious salmon anemia virus

Abstract

A previous study showed that a plasmid expressing IFNa (pIFNa) strongly enhanced protection and antibody production of a DNA vaccine against infectious salmon anemia virus (ISAV) in Atlantic salmon. The vaccine consisted of a plasmid (pHE) expressing the virus hemagglutinin-esterase as an antigen. To increase the understanding of the adjuvant effect of pIFNa, we here compared transcriptome responses in salmon muscle at the injection site at week 1 and 2 after injection of pIFNa, pHE, plasmid control (pcDNA3.3) and PBS, respectively. The results showed that the IFNa plasmid mediates an increase in gene transcripts of at least three major types in the muscle; typical IFN-I induced genes (ISGs), certain chemokines and markers of B- cells, T-cells and antigen-presenting cells. The latter suggests recruitment of cells to the plasmid injection site. Attraction of lymphocytes was likely caused by the induction of chemokines homologous to mammalian CCL5, CCL8, CCL19 and CXCL10. IFN may possibly also co-stimulate activation of lymphocytes as suggested by studies in mammals. A major finding was that both pcDNA3.3 and pHE caused responses similar to pIFNa, but at lower magnitude. Plasmid DNA may thus by itself have adjuvant activity as observed in mammalian models. Notably, pHE had a lower effect on many immune genes including ISGs and chemokines than pcDNA3.3, which suggests an inhibitory effect of HE expression on the immune genes. This hypothesis was supported by an Mx-reporter assay. The present study thus suggests that a main role for pIFNa as adjuvant in the DNA vaccine against ISAV may be to overcome the inhibitory effect of HE- expression on plasmid-induced ISGs and chemokines.

Transcriptome analyses of Atlantic salmon muscle genes induced by a DNA vaccine against salmonid alphavirus, the causative agent of salmon pancreas disease (PD)

“…The IFN-I response to pSAV is thus likely to be a response to plasmid DNA rather than to the viral proteins. The virus proteins expressed by pSAV do thus not seem to induce IFN-I such as the G-protein of the DNA vaccine against IHNV [ 5 , 8 ]. Moreover, pSAV does not inhibit the IFN-I response unlike hemagglutininesterase in the DNA vaccine against ISAV [ 5 , 8 ].…”

“…The analyses were carried out essentially as described earlier [ 5 ]. Nofima’s Atlantic salmon oligonucleotide microarray SIQ-6 (GEO Accession no.…”

“…The vaccine was a plasmid expressing the virus surface protein hemagglutininesterase (HE) and the IFN plasmid was shown to function as an adjuvant. A transcriptome analysis of genes induced at the muscle injection site by a plasmid encoding HE, plasmid vector without insert, and plasmid encoding IFNa was recently carried out [ 5 ]. The work showed that plasmid DNA induced a similar set of genes as the IFNa plasmid, but at a lower level.…”

“…It is likely that the adaptive immune system reacts to antigens as soon as they are expressed. Day 7 post injection was thus chosen as time point for harvest of mRNA since it represents early high level expression of plasmid encoded genes in the muscle [ 5 , 7 , 8 ].…”

Consequences of Haemorrhagic Smolt Syndrome (HSS) for the Immune Status of Atlantic salmon (Salmo salar L.) (Case Study)

“…Viral infections commonly activate a large group of genes involved in innate antiviral immunity termed VRG-virus responsive genes [19]. VRG can be induced with other agents, for example with bacterial DNA in the form of plasmids [20], and in theory this may complicate the conclusions. However, lack of VRG stimulation points to absence of a pathogenic virus in an active state.…”