Activation of the specific neurotrophin receptors TrkA, TrkB and TrkC influences the function of eosinophils

Background Recent studies have shown that nerve growth factor (NGF) can act on several immune cells as well as residential cells. But little is known about their role in modulating eosinophil function via activation of high-affinity receptors. Objectives The aim of this study was to assess whether eosinophils express functional receptors and if their function is influenced by NGF, brain-derived neurotrophic factor (BDNF) or neurotrophin-3 (NT-3). Methods Eosinophils were purified by negative immunoselection (purity > 96%). High-affinity neurotrophin receptors were demonstrated by reverse transcription polymerase chain reaction, western blotting and flow-cytometry analysis. Functionality of receptors was demonstrated by receptor phosphorylation after ligand binding. Eosinophils were incubated with NGF, BDNF and NT-3, and cells and supernatants were collected for measurement of the mediators IL-4, IL-5, IL-8, transforming growth factor (TGF)-beta(1), eosinophil cationic protein (ECP), eosinophil protein X (EPX) as well as eosinophil viability. Results Eosinophils expressed mRNA for neurotrophin receptors. Proteins were detectable by western blot and fluorescent-activated cell sorter analysis. The receptors were phosphorylated after stimulation with neurotrophins. After NGF stimulation, a significant increase in IL-4 was detectable. BDNF and NT-3 stimulation led to a significant increase in EPX. Eosinophil viability was not influenced. Conclusions Eosinophils express the functionally active receptors TrkA, TrkB and TrkC. Receptor activation stimulates eosinophils. This might be an additional pathway regulating inflammatory responses in allergic reactions.