Novel insights into the insect immune response to a natural DNA virus.. Insect immune response to a DNA virus.

Background: Little is known about the invertebrate innate immune’s response to DNA viruses. Here, we infect a commercially important pest moth species Plodia interpunctella with its naturally infecting DNA virus. We sequenced, assembled and annotated the complete transcriptome of the moth, and a partial transcriptome of the virus. We then tested for differential gene expression between moths exposed to the virus and controls. Results: We found 51 genes that were differentially expressed (DE) in moths infected with a DNA virus compared to controls. Gene set enrichment analysis revealed that cuticle proteins were significantly overrepresented in this group of genes. Interestingly, 6 of the 7 DE cuticle proteins were downregulated supporting the hypothesis that baculoviruses are able to manipulate its host’s immune response. In fact, an additional 29 of the 51 genes were also downregulated in infected compared with control animals, including a gram-negative binding protein. In contrast, genes involved in transposable element movement were upregulated after infection. Conclusions: We present the first experiment to measure gene expression in an insect after infection with a natural DNA virus. Our results indicate that cuticle proteins might be key genes underpinning the innate immune response to DNA viruses. Furthermore, the large proportion of genes that were downregulated after viral exposure suggests that this virus is actively manipulating the insect immune response. Finally, it appears that transposable element activity might increase during an immune response. Combined, these results provide much needed candidate genes in the innate immune response to DNA viral invaders.