SUPPRESSION BY CORTISOL OF THE MITOGEN-INDUCED PROLIFERATION OF PERIPHERAL BLOOD LEUCOCYTES FROM PLAICE, PLEURONECTES PLATESSA L.

Publisher Summary This chapter presents an investigation of the effect of cortisol on the mitogen-induced proliferation of peripheral blood leucocytes of plaice. Outbreaks of disease in fishes are frequently associated with environmental stressors, although a causal relationship between stressors and disease is less often established. As stressors commonly, but not universally, cause increased activity in the hypothalamo-pituitary-adrenocortical system, it has been proposed that corticosteroids are important mediators of the stressor's action. Treatment of fish with cortisol can cause increased incidence of disease, although it is questionable whether the plasma levels of steroid were physiological. The disease-related action of corticosteroids in mammals almost certainly includes immunosuppressive mechanisms such as macrophage inhibition, sequestration of lymphocytes, and inhibition of lymphocyte function. The fact that physiological levels are suppressive in vitro suggests that cortisol may function similarly in vivo . This steroid action may be a significant part of the mechanism by which stressors induce disease.