Assessment of splenic and peripheral lymphocyte population in broilers kept under a heat stress condition and treated or not with metyrapone and mifepristone

Abstract

Neuroimmunomodulation studies showed the existence of a tied and bidirectional relationship between the Central Nervous System (CNS) and the Immune System (IS); the major links of these interconnected systems are thought to be the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic autonomous nervous system (SNAS). Corticosterone and catecholamines were shown to play relevant and important roles in this communication, mainly during stress. Indeed, they are commonly known to modulate cytokines gene transcription and, consequently they may change immune and inflammatory processes such as the phagocytic activity of macrophages and heterophiles. In particular, the Th1 / Th2 cytokine profile balance is taken as pivotal for immune activity changes induced by stress. Chickens are extremely sensitive to environmental stressors; high environmental temperatures - a reality in production systems, have been reported to decrease animal's productive performance, here represented by the reduction they induce on food conversion, carcass quality and weight and incidence of clinical and/or subclinical infections, mainly at the intestinal level. Since these stressful situations negatively impact poultry production they might have also negative consequences in the Brazilian trade and economy. We showed in our laboratory that heat or overcrowding stress applied to broilers suppressed they immune system activity, leading to failures in the chickens response to vaccination and immune organ development. Heat stress also decreased chickens resistance to Salmonella invasion. These effects were taken as being a consequence of HPA-axis and/or SNS activations. Therefore, the purpose of this project is to use pharmacological tools such as mifepristone, an antagonist of glucocorticoid receptors and metyrapone, an inhibitor of corticosterone production to analyze HPA-axis involvement on heat stress induced effects in spleen and peripheral lymphocytes of broiler chickens as well as on animal's performance. (AU)