Production of rabbit antisera against recombinant MHC class II β chain and identification of immunoreactive cells in Atlantic salmon (Salmo salar)

In the present work, rabbit antisera recognising the Atlantic salmon (Salmo salar) MHC class II β chain polypeptide were produced and used in immunoblotting, immunohistochemistry and immunogold electron microscopy. A construct encoding the β1 and β2 domains fused to the E. coli protein thioredoxin was used to express the recombinant MHC class II β chain. Immunoblotting revealed a band of approximately 30 kDa in total protein samples from head kidney, spleen, gills, thymus and blood leukocytes, while being absent in muscle. The distribution of MHC class II positive cells was immunohistochemically demonstrated in Atlantic salmon epithelial and haemopoietic tissues. Ultrastructural demonstration of immunoreactive organelles in mid-kidney cells was performed by immunogold electron microscopy. The results indicate expression in lymphocytes, macrophages, epithelial cells and endritic-like cells. This is the first study to address morphological MHC class II expression in a fish species.