Page - (000138) - in Biomedical Chemistry: Current Trends and Developments

Acute stress also orchestrates a massive redistribution of immune cells in the body, which is consistent with the critical role the immune system has on survival; therefore, functions such as wound healing and immune surveillance (Dhabhar, 2012) would be enhanced during acute stress. Stress responsive hormones such as NE, corticosterone and epinephrine (EPI) influence many different subsets of immune cells. NE and EPI are released early in the stress response; while, NE increases leucocyte numbers, mobilizing immune cells, including neutrophils, monocytes, and lymphocytes to enter the blood; EPI mobilizes neutrophils and monocytes into the blood, but directs lymphocytes to leave the circulation to specific tissues, such as skin. Corticosterone is then released and mobilizes immune cells to leave the blood towards tissues. Acute restraint stress increases the numbers of T cells, such as memory and effector helper cells, in sentinel lymphnodes (Dhabhar & Viswanathan, 2005). Stress-induced increments in T cell memory may stimulate the increase of infiltrating lymphocytes and macrophage detected on antigen re-exposure several months later and this process is driven by increased levels of CD4+ T helper (Th) cells type 1 (Th1) cytokines IL-2, interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α). 2.2.3 The Effect of Chronic Stress and MDD in Dysregulating the Core Stress System In chronic or long-term stress the physiological stress response continues long after the stressor has ended, resulting in a prolonged exposure to stress hormones and stress-related reactions, or is activated repeatedly as a result of continued exposure to the stressor. Chronic activation of the HPA axis and sympathetic nervous system are common in MDD, melancholic subtype; circulating levels of cortisol are elevated and it is commonly accepted that the central CRH level is increased (or inappropriately non-suppressed for the level of hypercortisolism). Elevations of the cerebrospinal fluid (CSF) 24-hour levels of NE and plasma cortisol indicate that there is a persistent stress-system