Impact of stress on aged immune system compartments: Overview from fundamental to clinical data.

Life expectancy is continuously increasing due to major progress in preventing, delaying or curing various pathologies normally encountered in old age. However, both scientific and medical advances are still required to understand underlying cause of the disparate comorbidities occurrence with aging. In one hand, aging profoundly impairs the immune system; it is characterized by many changes in haematopoiesis, adaptive and innate systems, associated with pro-inflammatory environment. In another hand, stressful events (acute or chronic) can also impact the immune system through the secretion of hormones, which are also altered with aging. The field of psychoneuroimmunology is now providing evidences that in acute medical conditions, elderly people are not equal in their responses to stressors depending on many extrinsic and intrinsic factors. These parameters could interfere with elderly's ability to mount an effective immune response. The objective of this review is to provide an overview of the literature (from fundamental to clinical observations) to draw a parallel between immune dysregulation caused by stress or by aging. Understanding this entanglement could enable us to target fundamental age-related pathways and thus open new avenues in improving both lifespan and health span.