Immune-Related Gene Expression Profiling of Pacific Bluefin Tuna During Early Development

Pacific bluefin tuna (Thunnus orientalis) is one of the most important fishery resources in the north Pacific. In the last decade, because of the high commercial value at fishery markets, bluefin tuna farming is rapidly growing and larviculture of this species has been developed in Japan. However, larviculture of the bluefin tuna has faced some infectious disease challenges, especially by red sea　bream iridovirus. Therefore, our understanding of the host defense mechanisms of bluefin tuna juveniles would be important for developing effective control methods against infectious diseases in larviculture. However, to date, there are few studies on the immune system of the bluefin tuna. In this study, to understand the ontogeny of immunity in the bluefin tuna, we explored expression patterns of immune-related genes of the blufin tuna during 1–25 days post-hatch (dph) using a 44K microarray. Our microarray analyses monitored the transcription of approximately 28,000 genes during bluefin tuna development. The results showed that the innate immune genes, complement components and C-type lectin, were already expressed at very early developmental stages (3 dph–5 dph) , while the expression of adaptive immune genes, MHC class II, immunoglobulin light-chain and T cell receptors, were highly expressed at 25 dph. These results provide the first insights into the ontogeny of the immune system in the bluefin tuna and will help in the planning of future vaccination strategies in order to induce protective immune responses at the earliest time possible.