Biological Rhythms and the HPA Axis in Psychoneuroimmunology

Abstract

Intrinsic biological rhythms are the key features of the whole body complexity with the essential roles in health and aging. In the regulations of the immune system, more and more evidences have shown that circadian rhythms play a critical role. A variety of immune variables have been found to go through daily fluctuations. To translate the understanding of such mechanisms into better clinical outcomes, some potential methods have been proposed to moderate homeostatic circadian operations, such as the reprogramming of biological rhythms. Using systems biology methods, a multiscale systems understanding of circadian systems can be formed, expanding from the molecular level to the whole organism. With their effects on the physiology, behaviors, and pathology in certain conditions, the circadian and ultradian rhythms in the hypothalamic–pituitary–adrenal (HPA) axis have profound impacts on health and diseases. The joined molecular feedback and feedforward loops are essential in such neuroendocrine-immune networks, allowing for synchronized functions that may be essential to optimize the immune reactions. The psychoneuroimmunology (PNI) studies of anxiety, posttraumatic stress, and obsessive compulsive disorders have emphasized the dysfunctions in the immune system and the HPA axis. The dysregulation of the rhythmic patterns in the HPA axis has been closely associated with the pathophysiology of depression. While it is hard to use traditional neuroendocrine methods to represent and predict metabolic health, the dynamical systems approach may be appropriate to analyze the resilience and robustness of the HPA-leptin axis.