NGF was initially isolated in the mouse submandibular gland as a 7S complex composed of three non covalently linked subunits, α, β, and γ. Both the α and γ subunits of NGF are members of the kallikrein family of serine proteases while the β subunit, called βNGF or 2.5S NGF, exhibits all the biological activities ascribed to NGF. Recombinant human βNGF is a homodimer of two 120 amino acid polypeptides. The human protein shares approximately 90% homology at the amino acid level with both the mouse and rat βNGF and exhibits cross species activity.

Image: Fully extended DRG growth cone growing on a laminin-coated tissue culture plate in the presence of human β-NGF.

NGF is a wellcharacterized neurotropic protein that plays a critical role in the development of sympathetic and some sensory neurons in the peripheral nervous system. In addition, NGF can also act in the central nervous system as a trophic factor for basal forebrain cholinergic neurons. NGF has also been shown to have biological effects on nonneuronal tissues. NGF is mitogenic for a factordependent human erythroleukemic cell line, TF1NGF has been found to increase the number of mast cells in neonatal rats and to induce histamine release from peritoneal mast cells. NGF will enhance histamine release and strongly modulate the formation of lipid mediators by basophils in response to various stimuli. NGF will also induce the growth and differentiation of human B lymphocytes as well as suppress apoptosis of murine peritoneal neutrophils. These results, taken together, suggest that NGF is a pleiotropic cytokine which, in addition to its neurotropic activities, may have an important role in the regulation of the immune system.