Stress system--organization, physiology and immunoregulation

Stress is defined as a state of threatened homeostasis. The principal effectors of the stress system include corticotropin-releasing hormone, arginine vasopressin, the glucocorticoids, and the catecholamines norepinephrine and epinephrine. Activation of the stress system leads to adaptive behavioral and physical changes. The principal stress hormones glucocorticoids and catecholamines affect major immune functions such as antigen presentation, leukocyte proliferation and traffic, secretion of cytokines and antibodies, and selection of the T helper (Th) 1 versus Th2 responses. A fully fledged systemic inflammatory reaction results in stimulation of the stress response, which in turn, through induction of a Th2 shift protects the organism from systemic overshooting with Th1/pro-inflammatory cytokines. Stress is often regarded as immunosuppressive, but recent evidence indicates that stress hormones influence the immune response in a less monochromatic way--systemically they inhibit Th1/pro-inflammatory responses and induce a Th2 shift, whereas in certain local responses they promote pro-inflammatory cytokine production and activation of the corticotropin-releasing hormone-mast cell-histamine axis. Through this mechanism a hyper- or hypoactive stress system associated with abnormalities of the systemic anti-inflammatory feedback and/or hyperactivity of the local pro-inflammatory factors may play a role in the pathogenesis of chronic inflammation and immune-related diseases.