Noradrenaline reduces the stimulatory effect of interleukin-1 alpha on reactive oxygen species production by oyster immunocytes

A growing body of evidence suggests that interleukin-1 alpha (IL-1 alpha) i s present in invertebrates. Both invertebrate and human IL-1 alpha can bind to invertebrate receptors and stimulate invertebrate immune functions. The present study shows that IL-1 alpha increases reactive oxygen species (ROS ) production by oyster immunocytes. However, physiological doses of noradre naline (NA) exert a suppressive effect on IL-1 alpha stimulation in vitro. The beta -adrenoceptor agonist isoproterenol mimicked the effects of NA and the beta -adrenoceptor antagonist propanolol blocked the NA-induced suppre ssion of hemocyte responsiveness to IL-1 alpha. The type IV phosphodiestera se inhibitor rolipram acted in synergy with isoproterenol to reduce hemocyt e response to IL-1 alpha and the protein kinase A inhibitor H-89 suppressed the effects of isoproterenol. These results suggest that circulating NA im pairs IL-1 alpha -stimulation of oyster hemocyte via a beta -adrenoceptor/c yclic AMP/protein kinase-A signaling pathway. Considering that mollusc immu nocytes secrete NA, an autocrine regulatory loop may also modulate the abil ity of these cells to respond to IL-1 alpha.