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Effects of TGF‐β on Eosinophil Chemotaxis

Transforming growth factor‐β (TGF‐β), which can decrease the effects of interleukin (IL)‐3, IL‐5 and granulocyte–macrophage colony‐stimulating factor (GM‐CSF) on eosinophil viability, has been shown to be chemotactic for neutrophils. However, there is little information on its effects on eosinophil chemotaxis. Because TGF‐β has recently been found in increased concentrations in asthmatic sputum, we investigated whether TGF‐β could influence eosinophil migration and eosinophil viability. Purified eosinophils from normal donors were incubated with increasing concentrations of TGF‐β. Chemotaxis was measured with a modified Boyden chamber technique. In addition, eosinophils were incubated for 96 h with either IL‐3, IL‐5 or GM‐CSF (1 ng/ml) together with increasing concentrations of TGF‐β. Eosinophil viability was then determined with propidium jodide and flowcytometry. Eosinophil chemotaxis was significantly increased in the presence of TGF‐β in concentrations between 10−9 and 10−4 μg/ml. The optimal concentration of TGF‐β in this assay was between 10−9 and 10−8 μg/ml. The chemotactic effect of TGF‐β diminished when higher as well as lower concentrations (between 10−12 and 10−3 μg/ml) were employed. In contrast, inhibition of eosinophil survival induced by IL‐3, IL‐5 and GM‐CSF reached its maximum at concentrations of TGF‐β between 10−4 and 10−3 μg/ml. From these data we conclude that TGF‐β in low concentrations can induce eosinophil chemotaxis whereas higher concentrations reduce eosinophil survival mediated by IL‐3, IL‐5 and GM‐CSF.