Nonclassical MHC class I L-lineage genes in Atlantic Salmon (Salmo salar L.): An investigation into transcriptional induction and cell type-specific expression patterns of different L-lineage subgroups

Abstract

The world's population is growing, and so is the world's food demand, underpinning the need for sustainable food production. Over the last few decades, Norwegian aquaculture production of Atlantic Salmon (Salmo Salar L.) and rainbow trout (Oncorhynchus mykiss) expanded rapidly. Unfortunately, today’s fish health situation is challenging due to virus infections, among other reasons. Today's virus vaccine is inadequate and doesn’t prevent viral disease outbreaks in the field. Detailed knowledge of how the salmon immune system combats viruses is still limited, and a better understanding is needed to make an efficient vaccine. When a virus infects a cell, the antigen from the virus is presented on a specialised complex called a Major Histocompatibility complex (MHC) class I by the infected cell. The MHC molecule interacts with T-cells that meditate an immune response. There are identified one classical MHC class I gene and several non-classical MHC class I genes in Atlantic Salmon. Compared to a classical MHC gene, the non-classical are not polymorphic and may present a more conserved structure to immune cells during an infection. There are identified six different functionally expressed non-classical MHC class I L-lineage genes in Atlantic Salmon. In this thesis, head kidney leucocytes (HKL) from Atlantic salmon were stimulated in vitro with IFNs and viral mimics, resulting in individual upregulation off L-lineage gene expression. Co-stimulation showed an antagonistic effect on the L-lineage subtypes LIA and LGA. Furthermore, by inhibiting JAK in the JAK/STAT signalling pathway, the gene expression decreased when stimulated in vitro, suggesting that the JAK/ STAT pathways probably have an essential role in regulating the gene expression of non-classical MHC class I L-lineage genes. To further investigate what cells express the different L-lineage genes, an optimised MACS was used to separate Macrophage-like cells, non-B cell lymphocytes and IgM-positive B-cells. In all different cell populations, LIA, LGA and LDA were expressed. However, the MAC-sorting still needs more optimisation before cell type-specific L-lineage gene expression can be implied.