Nerve growth factor: a neurokine orchestrating neuroimmune-endocrine functions.

Nerve growth factor (NGF) is widely recognized as a target-derived factor responsible for the survival and maintenance of the phenotype of specific subsets of peripheral neurons and basal forebrain cholinergic nuclei during development and maturation. Other NGF-responsive cells are now known to belong to the hemopoietic-immune system and to populations in the brain involved in neuroendocrine functions. The concentration of NGF is elevated in a number of inflammatory and autoimmune states in conjunction with increased accumulation of mast cells. Mast cells and NGF appear to be involved in neuroimmune interactions and tissue inflammation. Mast cells themselves are capable of producing and responding to NGF, suggesting that alterations in mast cell behavior may trigger maladaptive neuroimmune tissue responses, including those of an autoimmune nature. Moreover, NGF exerts a modulatory role on sensory nociceptive nerve physiology in the adult, and appears to correlate with hyperalgesic phenomena occurring in tissue inflammation. NGF can thus be viewed as a multifactorial modulator of neuroimmune-endocrine functions.