Adrenergic regulation of the innate immune response in common carp ( Cyprinus carpio L.)

► The β 2a adrenergic receptor gene is expressed in carp leukocytes. ► β 2a adrenergic receptor expression is regulated upon immune stimulation. ► Adrenaline inhibits production of radical oxygen species and nitric oxide. ► Adrenaline reduces expression of pro-inflammatory mediators. Catecholamines exert their physiological actions through α and β adrenergic receptors (ARs). As ARs are not exclusively expressed on neuroendocrine cells, but also on leukocytes, they may facilitate neuroendocrine modulation of immune responses. We sequenced the β 2a-AR in common carp, and studied its expression profile and involvement in the regulation of teleost innate immune responses. β 2a-AR messenger RNA was found to be constitutively expressed in brain areas, especially in the preoptic nucleus (NPO, homologous to the mammalian hypothalamus), and in immune organs. During the active phase of an in vivo inflammatory response, induced by i.p. zymosan treatment, β 2a-AR gene expression was up-regulated in the peritoneal leukocytes. Additionally, adrenaline in vitro reduced the synthesis of oxygen radical species and nitric oxide, while it enhanced arginase activity in fish phagocytes. Furthermore, in vitro adrenaline administration inhibited expression of pro-inflammatory cytokines, chemokines and their receptors. It is therefore hypothesized that adrenaline will down-regulate phagocyte skewing toward classical/innate polarization.