Nerve growth factor or IL-3 induces more IL-13 production from basophils of allergic subjects than from basophils of nonallergic subjects

Background: Studies show that nerve growth factor (NGF) exhibits immunomodulatory activity. This neurotrophin is found at high levels in the serum of asthmatic individuals, is released during allergic reactions, and is reported to augment in vitro histamine and leukotriene C4 release by human basophils. Objective: Because basophils represent a substantial source of IL-4 and IL-13, we tested the effects of NGF on the secretion of these cytokines by cells prepared from allergic subjects and cells prepared from nonallergic subjects. Methods: Cytokine and histamine were measured in culture supernatants by ELISA and fluorimetry, respectively. Both real-time RT-PCR and conventional RT-PCR were used to measure IL-13 mRNA expression. NGF receptor expression was determined by 2-color flow cytometry. Results: Basophil suspensions from allergic subjects secreted some 2.5-fold greater levels of IL-13 when cultured with NGF than did cells prepared from normal control subjects. Flow cytometry revealed no significant differences in TrkA receptors on basophils to explain these findings. The levels of IL-13 secreted by the 2 groups of donors also differed when cells were activated with IL-3 but not when they were activated with anti-IgE antibody. Both NGF and IL-3 failed to induce IL-13 in cell cultures depleted of basophils, suggesting that the measurable IL-13 was indeed basophil-derived. Real-time RT-PCR showed an average induction of IL-13 message above medium control that was 4.3 (± 1.7)-fold with NGF and 8.9 (± 3.7)-fold with IL-3. Finally, NGF priming resulted in a remarkable enhancement of IL-13 induced by anti-IgE. This was significantly greater than the priming observed for either the IL-4 or histamine when this stimulus was used. Conclusion: NGF (like IL-3) can both directly stimulate IL-13 secretion and modulate IgE-mediated responses in basophils. Its enhanced effect on cells from allergic individuals raises the importance of this cytokine in the pathogenesis of allergic disease.