Cloning and expression of TNF-α, IL-1β and COX-2 in an anadromous and landlocked strain of Atlantic salmon ( Salmo salar L.) during the smolting period

The parr–smolt transformation involves complex modulation of immune parameters, affecting both cell populations and humoral factors. The expression of cytokines was studied in salmon cells and tissues during this period using an anadromous and a landlocked freshwater resident dwarf strain of Atlantic salmon ( Salmo salar L.). The constitutive activity of three immunoregulatory genes encoding the cytokines tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) and the cyclo-oxygenase (COX) isoform COX-2 was investigated in head kidney, spleen and gill tissue from healthy, unvaccinated fish by real-time PCR. The TNF-α gene was generally lower expressed than COX-2 and IL-1β1, which were approximately expressed at equal levels and constitutive expression was seen for COX-2 and IL-1β1 in all tissues examined and at all sampling dates. The expression of all three genes in head kidney and spleen tissue seemed to be highest at the sampling in May for both strains around the time of seawater transfer suggesting an influence of smolting related hormones on cytokine expression. The gill tissue experienced the highest expression of IL-1β1 and COX-2 at all sampling dates indicating that this organ is immunologically important.