Nerve growth factor: An important molecule in allergic inflammation and tissue remodelling

Background: Several studies provide evidence that nerve growth factor (NGF) has an expanding role in neuroimmune interactions. Methods: We review our data on circulation levels of NGF in allergic diseases as well as on the relationships between this neurotrophin and primary and secondary effector cells of allergic inflammation. Results: In vernal keratoconjunctivitis, a close relationship exists between the increased NGF plasma values and the number of mast cells infiltrating the conjunctiva. NGF serum values are also increased in other allergic diseases and asthma, and are related to the severity of the inflammatory process and disease. Human CD4+ T cell clones (preferentially of activated Th2 type) produce and release NGF, and express high-affinity NGF receptors. NGF is preformed in and can act on human peripheral blood eosinophils to preferentially release inflammatory mediators. Immunoreactivity for high affinity NGF receptors is present both in basal epithelial cells and in the inflamed stroma of the allergic conjunctiva. Topical administration of NGF results in a complete healing of neurotophic corneal ulcers in man, thus suggesting a profound effect of NGF on human fibroblasts and extracellular matrix. Conclusion: Data presented suggest that NGF is an important molecule in allergic inflammation and tissue remodelling occurring in allergic diseases.