In vitro expansion of human basophils by interleukin-3 from granulocyte colony-stimulating factor-mobilized peripheral blood stem cells

Background: A number of studies support the belief that human basophils play an important role in allergic inflammation. The exact mechanism of basophil activation at the site of allergic inflammation, however, has not been well understood, mainly due to their low number in blood and difficulty in obtaining a sufficient number of highly purified basophils for investigation. Objective: The purpose of this study is to expand human basophils in vitro with high yield and purity by culturing peripheral blood stem cells (PBSCs). Methods: We collected PBSC-rich mononuclear cells containing CD34⁺ cells (0.15-4.9%) by leukapheresis from patients with malignant lymphoma and lung cancer during haematopoietic recovery after chemotherapy plus granulocyte colony-stimulating factor-induced mobilization. PBSC-rich mononuclear cells were cultured in the presence of IL-3. Results: When PBSC-rich mononuclear cells containing more than 1% of CD34⁺ cells were cultured, 20.0-83.3% of the cells, mostly with a yield of > 10%, were metachromatic cells after 3 weeks of culture. These cells resembled mature peripheral blood basophils morphologically when examined by light and electron microscopy. Flow cytometric analysis showed that they expressed both FcεRI and FcγRII. FcεRI cross-linking resulted in intracellular calcium mobilization, histamine release and synthesis of cysteinyl leukotrienes. The intracellular histamine content and the release of these chemical mediators triggered by anti-IgE antibodies were comparable to those of peripheral blood basophils. Conclusion: These findings suggest that PBSC-derived basophils expanded in vitro are morphologically and functionally mature and will be a useful tool for the analysis of basophil functions.