Increased proliferation of eosinophil clusters in myelodysplastic syndromes.

A patient with myelodysplastic syndromes (MDS) developed eosinophilia during treatment with recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF). To study the mechanism of this eosinophilia, we investigated the proliferation of eosinophil colony-forming units (CFU-Eo) in nine patients and four healthy controls. Eosinophil clusters increased significantly in the patients (P < 0.01) compared with controls, but eosinophil colonies were not different between controls and MDS patients. In addition, the eosinophil clusters were significantly increased with rhGM-CSF in MDS patients compared with controls, although serum GM-CSF concentrations were similar in both groups. These results suggest that eosinophil clusters are increased in MDS either through abnormal progenitor proliferation or hypersensitivity to GM-CSF.