CD8α and CD8β in Atlantic halibut, Hippoglossus hippoglossus: Cloning, characterization and gene expression during viral and bacterial infection

CD8 is expressed on cytotoxic T-cells where it functions as a co-receptor for the TCR by binding to MHC class I proteins that present peptides on the cell surface. In this study we describe the cloning and sequencing of full length cDNAs encoding CD8α and CD8β from Atlantic halibut (Hippoglossus hippoglossus L.) and subsequent isolation and characterization of the CD8α and CD8β genes. The predicted halibut CD8α and CD8β proteins are similar to those of mammals and other fish. Real time RT-PCR revealed that the highest levels of CD8 mRNA were found in the thymus, while some expression was also seen in the spleen, the gills, and the anterior and posterior kidney. In situ hybridization confirmed that the halibut thymus contained numerous CD8α and CD8β expressing cells, while the anterior kidney had no CD8α positive cells but only a few CD8β expressing cells. Only moderate changes in CD8 mRNA expression in other organs during either nodavirus or Vibrio anguillarum infection were observed. Both CD8α and CD8β were significantly (P < 0.05) down-regulated in spleen at 48 h compared to their levels at 12 h post-infection with nodavirus and V. anguillarum.