Molecular Mechanism underlying Eosinophil Differentiation in Bronchial Asthma

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Allergic late-phase reactions provoked by specific antigens are associated with intense eosinophil infiltration into the site of antigen administration. Because eosinophils contain a large amount of cytotoxic proteins in their granules and is believed to be involved in the pathogenesis of allergic inflammation, the downregulation of eosinophil differentiation is considered to be important for the inhibition of allergic inflammation. While it is well known that IL-5 plays a critical role in the eosinophil development, it is unknown about the molecular mechanisms of IL-5-induced eosinophil development. Recently, it has been demonstrated that, using IL-5Rα transgenic mice, IL-5 does not transduce a specific signal for the eosinophil development but simply transduces a proliferative signal to eosinophil progenitors that express IL-5Rα specifically. Therefore, it is essential to understand the regulatory mechanisms of IL-5Rα expression in eosinophils to prevent allergic inflammation.To determine the molecular mechanism underlying the cell lineage-specific expression of IL-5Rα in eosinophils, we developed a retrovirus-mediated mammalian one hybrid system. In this system, BaF3 cells (Thy1.2) were transfected with Thy1.1 cDNA under the control of IL-5Rα promoter (BaF3-P1-Thy1.1 cells) and then BaF3-P1-Thy1.1 cells were retrovirally transfected with cDNA library of an eosinophilic cell line (AML14.3D10 cells). After 2 weeks of culture, Thy1.1-positive cells were purified by magnetic cell sorting and cDNAs in the retrovirus vector in the Thy1.1-positive cells were isolated by PCR. By two cycles of the screening, we isolated 25 cDNAs. Now, we are performing the experiments to confirm the ability of cDNAs to induce the expression of IL-5Rα. In the near future, we believe that genes that regulate the eosinophil development can be isolated from the cDNAs and that the mechanism of eosinophil development is uncovered.