Neurohormonal-cytokine interactions: implications for inflammation, common human diseases and well-being

The neuroendocrine system affects the immune system through the neuroendocrine humoral outflow via the pituitary, and through direct neuronal influences via the sympathetic, parasympathetic (cholinergic) and peptidergic/sensory innervation of peripheral tissues. Circulating hormones or locally released neurotransmitters and neuropeptides regulate major immune functions, such as antigen presentation, antibody production, lymphocyte activity, proliferation and traffic, and the secretion of cytokines including the selection of T helper (Th)1 or Th2 cytokine responses. During inflammation, the activation of the stress system, through induction of a Th2 shift protects the organism from systemic "overshooting" with Th1/pro-inflammatory cytokines. Under certain conditions, however, stress hormones, substance P, ATP and the activation of the corticotropin-releasing hormone/substance P-histamine axis may actually facilitate inflammation, through induction of interleukin (IL)-1, IL-6, IL-8, IL-18, tumor necrosis factor (TNF)-alpha and CRP production. Thus, a dysfunctional neuroendocrine-immune interface 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 atopic/allergic and autoimmune diseases, obesity, depression and atherosclerosis. Better understanding of the neuroendocrine control of inflammation may provide critical insights into mechanisms underlying a variety of common human immune-related diseases.