A novel method for procuring a large quantity of mature murine eosinophils in vivo

Eosinophils are rare hematopietic cells that normally constitute only 1~3% of peripheral blood leukocytes. It would be of help for the purpose of research to obtain a large quantity of eosinophils. In this study, we wanted to develop a novel strategy to induce massive expansion of murine eosinophils in vivo, based on the observation showing that treatment of IL-33 induces eosinophilia in mice. We generated an EL-4 lymphoma cell line (herein named EL-4-IL-33) that was engineered to secrete an active form of IL-33. We found that Siglec-F(+) granulocyte numbers increased by 1850-fold in the peritoneal cavity 10 days after inoculation with 1×10⁷ EL-4-IL-33 cells. This number corresponds to 74-fold increase, as compared with the number of Siglec-F(+) granulocytes in mice that received wild-type EL-4 cells. Siglec-F(+) granulocytes expanded by IL-33 had the circular nucleus and expressed eosinophil-specific genes. They also showed some functional characteristics of eosinophils in that they had the ability to respond to IL-5 for survival and eotaxin-1 for chemoattaxis and to produce bioactive eosinophil peroxidase, suggesting that these cells are genuine eosinophils. Our results indicate that sustained secretion of IL-33 by lymphoma cells in the peritoneal cavity is highly effective in increasing peritoneal eosinophil numbers. Therefore, our simple method to obtain eosinphils on a large scale might be of value for eosinophil studies.