Synergism of IL-3, IL-5, and GM-CSF on eosinophil differentiation and its application for an assay of murine IL-5 as an eosinophil differentiation factor.

In order to elucidate the mechanisms of eosinophil differentiation, we examined the effects of combinations of interleukin 5 (IL-5) with IL-3 and granulocyte-macrophage colony-stimulating factor (GM-CSF) on in vitro differentiation into eosinophils from bone marrow cells of ICR mice. When the amount of added IL-5 was kept constant, IL-3 exhibited dose-dependent production of eosinophils both in the absence and presence of low doses of GM-CSF. In contrast, IL-5 plus GM-CSF showed highly enhanced production of eosinophils, and eosinophil production maximized at a concentration between 10 and 20 U/ml and decreased at higher concentrations. When IL-3 and GM-CSF were kept constant at concentrations of 20 U/ml and 10 U/ml, respectively, the number of eosinophils increased linearly in IL-5-dependent manner in a range from 0.3 to 30 U/ml. These results suggest that IL-3 and GM-CSF act synergistically with IL-5 in in vitro eosinophil differentiation. In addition, we propose a new method for quantifying eosinophil differentiation activity of IL-5.