Neuroimmune Crosstalk in CNS Disorders: The Histamine Connection.

The neuroimmune system represents a dense network of biochemical signals associated with neurotransmitters, neuropeptides, neurohormones, cytokines, chemokines, and growth factors synthesized in neurons, glial cells and immune cells, to maintain systemic homeostasis. Endogenous and/or exogenous, noxious stimuli in any tissue are captured by sensor cells to inform the brain; likewise, signals originating at the central nervous system (CNS) level are transmitted to peripheral immune effectors which react to central stimuli. This multidirectional information system makes it possible for the CNS to respond to peripheral damage and for alterations in brain function to be reflected in peripheral immune changes. Different CNS disorders, such as anxiety, depression, psychosis, stroke, Alzheimer's disease, Parkinson's disease, attention-deficit hyperactivity disorder, migraine, epilepsy, vascular dementia, mental retardation, cerebrovascular encephalopathy, multiple sclerosis, brain tumors, cranial nerve neuropathies, mental retardation and post-traumatic brain injury exhibit changes in CD3, CD4, CD7, HLA-DR, CD25, CD28, and CD56 immune markers. Histamine is an important pleiotropic factor in neuroimmune regulation. This biogenic amine shows age-and sex-dependent changes in the CNS, and is significantly altered, together with interleukin- 1β and TNF-α, in Alzheimer's disease and other neurodegenerative disorders in which neuroinflammation appears to be an aggravating phenotype. Therapeutic intervention to halt progression of deleterious neuroinflammatory reactions in CNS disorders is a major challenge for molecular pharmacology in the future.