The production, storage and release of the neurotrophins nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3 by human peripheral eosinophils in allergics and non-allergics

Background Recent studies have shown that neurotrophins are produced by and can act on several immune-inflammatory cells. The origin of circulating as well as local neurotrophins is unknown. Objectives The aim of this study was to assess whether eosinophils of allergic and non-allergic donors produce, store and release the neurotrophic factors NGF, BDNF and NT-3. Methods Eosinophils were purified by negative immunoselection (purity > 96%) from allergic asthmatics and non-allergic donors (25 to 53 years). The presence of mRNA for neurotrophic factors was evaluated by reverse transcription PCR. Specificity was demonstrated by cloning products and sequencing. Stored NGF, BDNF and NT-3 was demonstrated by Western-blotting and flow cytometry. Eosinophils were incubated and supernatants were collected for measurement of neurotrophic factors after cell stimulation with PAF. Neurotrophin content in eosinophil lysates was determined by ELISA. Results Eosinophils demonstrate mRNA for neurotrophins. Proteins were detectable by Western blot and FACS analysis. Neurotrophins were found in the eosinophil lysates at different amounts comparing allergic and non-allergic donors. Cell stimulation with PAF (10(-8) -10(-5) M) after priming with GM-CSF leads to a dose-dependant release of NGF and BDNF. Conclusions Eosinophils store, produce and release NGF, BDNF and NT-3. They are a possible source of elevated neurotrophin levels found in allergy and asthma.