Biological characteristics of chronic eosinophilic leukemia cells with a t(2;5)(p23;q35) translocation.

We studied the biological features of eosinophils in a patient with chronic eosinophilic leukemia and a unique t(2:5)(p23;q35) translocation. Microscopic and cytochemical studies revealed no particular abnormalities, although more than 90% of the peripheral eosinophils had a density lighter than 1.080 g/ml. Clonogenic assay disclosed that myeloid progenitor cells possessed the translocation, although in vitro eosinophilopoiesis seemed normal, and there were also hematopoietic cells with a normal karyotype. In a surface marker study, EG1 was positive on 34.0% of the eosinophils, while EG2 positivity was only 0.5%. Eosinophilopoietic growth factors and adhesion molecules were virtually absent with the exception of GM-CSF and CD11b. Functional studies showed that chemotaxis for C5a was normal, although that for IL-2 or FMLP was attenuated. In addition, leukotriene C4 production was decreased while O2- production was intact. These findings indicated that our patient's eosinophils were not in an activated state despite their extreme hypodensity, and suggested that the leukemic eosinophils had slight defects of cellular function. These characteristics may have saved the patient from the multiple organ damage which occurs in typical hypereosinophilic syndrome.