Stress-related hormones modulate cytokine expression in the head kidney of gilthead seabream (Sparus aurata)

Neuro-endocrine and immune systems closely interact in fish, and their regulation is crucial for the maintenance of good health of cultured fish. We have used the seabream head kidney to study whether stress-related hormones can modulate the immune response. For this purpose, the effects of adrenaline, adrenocorticotropic hormone (ACTH) and cortisol on the expression of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) and the anti-inflammatory cytokine TGF-β1 were determined by means of quantitative real-time PCR on isolated head kidney cells. ACTH (150 ng mL⁻¹) caused an acute increase of TNF-α and IL-6 mRNA levels as well as an inhibition of IL-1β expression. The expression of the anti-inflammatory cytokine TGF-β1 was also increased, although in a lower extent. Adrenaline (1 μM) early effects were only clear inhibiting IL-1β expression but not TNF-α, IL-6 or TGF-β1 mRNA levels, while a longer exposure to the hormone inhibited all cytokines. Moreover, cortisol (50 and 100 ng mL⁻¹) reduced the expression of all cytokines in a dose-dependent manner. Bacterial lipopolysaccharide (LPS) stimulated IL-1β expression and inhibited that of the anti-inflammatory TGF-β1, although it was ineffective on TNF-α and IL-6. In addition, adrenaline and cortisol decreased the LPS-stimulated IL-1β expression, further demonstrating their previously reported anti-inflammatory effects. The combination of ACTH and LPS, on the other hand, did not affect LPS-stimulated IL-1β expression but was effective increasing TNF-α expression. Taking all these results in consideration, we conclude that the expression of pro- and anti-inflammatory cytokines in the seabream head kidney is highly influenced by stress-related hormones, thus indicating an important role for the endocrine system in the modulation of the immune response in teleost fish.