γδ T cells in Atlantic salmon: Insight into the tissue distribution and gene usage of distinct TRG genes using molecular analysis

Abstract

Salmon farming is among the fastest growing food production in the world, and what was once a luxury food is now among the most popular fish species in Europe and Asia. With the rapid growth and increasing demand, the salmon industry is, in addition to other factors, highly dependent on vaccines to ensure a sustainable practice. It is therefore important to fully understand the mechanisms of the adaptive immune responses against pathogens. The adaptive immune system in jawed vertebrates consists of both B- and T cells, and the focus in this study has been on a specific populations of T cells, namely γδ T cells. Previous mapping of the TRG- loci revealed 7 constants (C) regions, where TRGC1, TRGC2, TRGC3 and TRGC5 is functionally expressed in the tissue. To study the expression and distribution of TRG in Atlantic salmon, the basal expression of TRGC genes in different tissues was measured with qPCR analysis. Spleen and head kidney leukocytes (SPLs and HKLs) had the overall highest expression of all TRGC genes, along with peripheral blood leukocytes (PBLs). Following stimulation with a T cell mitogen, upregulation of TRG was observed in several tissues, and the results also showed great expression variation between the different TRGC genes. The highest expressed TRGC gene expression was TRGC3, and the lowest expressed TRGC gene was TRGC2. In addition, PrimeFlow RNA assay was for the first time conducted with Atlantic salmon cells, by utilizing IgM, TRD and TRG specific probes. Consistent with qPCR analysis, PrimeFlow analysis revealed the highest expression of TRG in SPLs. The flow cytometry analysis revealed successful staining with probes, as well as surprising results, including the detection of a high intensity staining IgM positive subpopulation.