Inhibitory Effect of Transforming Growth Factor β1 on Cytokine-Enhanced Eosinophil Survival and Degranulation

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Abstract
The effects of transforming growth factor (TGF) β1 on cytokine-enhanced eosinophil survival and degranulation were investigated in vitro to determine whether it is an inhibitory regulator of allergic inflammation. Peripheral blood eosinophils purified by Percoll density gradient centrifugation and the CD 16 negative selection technique were incubated in the presence of eosinophil-activating cytokines (interleukin-5 (IL-5), IL-3, granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon (IFN)-γ) with and without TFG-β1 for 1–3 days. On day 1, eosinophil protein X release was measured by radioimmunoassay. Eosinophil viability on day 3 was determined by staining the cells with fluorescein diacetate and propidium iodide, and on the same day DNA was extracted and subjected to gel electrophoresis to test for fragmentation. TGF-β1 significantly inhibited eosinophil survival enhanced by IL-5, IL-3, GM-CSF and IFN-γ in a dose-dependent manner. The inhibitory effects of TGF-β1 on IL-5-enhanced survival was partially reversed by high concentrations of IL-5 and was completely neutralized with anti-TGF-β antibody. IL-5 inhibited DNA fragmentation of eosinophils in vitro. TGF-β reversed the effect of IL-5, indicating that TGF-β1 activates the pathway of apoptosis. TGF-β1 significantly suppressed eosinophil protein X release induced by IL-5. These results suggest that TGF-β1 may play a role in the modulation of allergic inflammation.

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