Stress on the immune system is mediated by several stress events in the immune system, each of which has a biological and psychological effect.
Stress is a negative psychological state that causes the body to go through various changes as a coping mechanism.
Psychological stress triggers a cascade of psychological and behavioral responses aimed at defending the host. During stressful events, the hormonal axis, which is made up of organs that make up the neuroendocrine system, controls stress responses and regulates body processes, the most important of which is the immune system. It interacts with the hypothalamus, an organ in the forebrain that controls various body processes, including the immune system. Therefore, it is imperative to understand the biological and psychological mechanisms on how stressors weaken one’s health. Stress can majorly be defined as a psychophysiological course that is majorly accompanied with negative emotional state resulting in a coping ability that is available for an individual. Stressors can either be physical, cognitive or a combination of both and these are further categorized into acute, sub-chronic and chronic stressors depending on their duration. Acute stressors last from minutes to hours, while sub-chronic stressors last less than one month. Anything that lasts from months to years is considered as a chronic stressor. In most cases, psychological stress initiates chord of psychological and behavioral responses which are intended to protect the host. This response often triggers both hypothalamic pituitary adrenal axis which is in constant communication feedback with the immune system and sympathetic branch of the autonomic nervous system, HPA, and SNS (sensory nervous system) respectively. Excitatory stimuli originate from the catecholaminergic axis in the limbic system and in the brainstem. These stimuli are collected by the paraventricular nucleus (PVN).
Also, the paraventricular nucleus of the hypothalamus (PVN) which are activated during stressful conditions can as well be triggered by any aminergic input from the locus coeruleus. Glutaminergic activity within the PVN stimulates the secretion of CRH (corticotropin-releasing hormone) from the nerve terminals. When SNS is activated, the result is an increased catecholamines secretion in the adrenal medulla and nerve terminals. Psychological stress additionally can affect other neuroendocrine frameworks like the HPGA (hypothalamic-pituitary-gonadal axis) which alters the regulation of menstrual cycle.
HPA axis, as well as autonomic nervous system, offers an interface between organ systems and psychological stress. The release of hormones that is stress-induced partially affects the function of immune system, and such effects can be seen in both the health and diseases. The balance existing linking humoral immunity that includes production of B cells and cell-mediated immunity that includes T cells, is significantly regulated by the cytokines which are produced by Th1 (T-helper) and Th2 (T-helper) cells. Th1 and Th2 cells are known as helper cells produced by subpopulations of CD4+ T-helper cells. Th1 cytokines support CMI regarding defending the host from intracellular parasites such viruses. Th2 cells, on the other hand, supports humoral immunity of the host defense against extracellular parasites.
According to Dhabhar et al., (p 5516) acute stress that enhances immune function can help in developing mechanism that is adaptive psychophysiologically and that increases immune protection from stressors. When viewed from the evolutionary perspective, dealing successfully with stressors is what enables one to survive, and therefore under al stressors, immunosuppression would not be adaptive. What the brain does is it recognizes the stressors and warns the body of the impending dangers thus promotes survival. In several cases, the several stressors that activate the immune response perhaps are those that have encountered previously. In such a case, the surveillance memories of the T-cells play a crucial role in initiating protection of the host. The grave effects of stress on human health are highly likely to be mediated by stress that is associated with type-1 or type-2 alterations of the cytokines. The immune cells are always on the permanent move within the surveillance pathways that transport them from the heart to different organs and back into the blood. This circulation ensures that there is an efficient network of immune defense and by stress weakening or strengthening this system; it is what leads to development or enhancement of certain ailments.
Dhabhar, F S, et al. “Effects of stress on immune cell distribution—dynamics and hormonal mechanisms.” The Journal of Immunology, vol. 154, no. 10, 15 May 1995, pp. 5511–5527., www.jimmunol.org/content/154/10/5511.