EOSINOPHIL HEMATOPOIETINS ANTAGONIZE THE PROGRAMMED CELL-DEATH OF EOSINOPHILS - CYTOKINE AND GLUCOCORTICOID EFFECTS ON EOSINOPHILS MAINTAINED BY ENDOTHELIAL-CELL CONDITIONED MEDIUM

Granulocyte-macrophage colony-stimulating factor (GM-CSF) was established as the constitutive and elicited human umbilical vein endothelial cell-derived eosinophil viability-sustaining factor. Stimulation of endothelium cell monolayers with IL-1-alpha (5 U/ml) increased the 48-h elaboration of GM-CSF from a mean of 3.2 to a mean of 8.2 pM (P < 0.05). Dexamethasone (100 nM) decreased the constitutive GM-CSF elaboration by 49% (P < 0.001) but did not diminish production by IL-1-alpha-stimulated endothelium. However, eosinophil viability decreased by 21 % in dexamethasone-pretreated IL-1-alpha-stimulated endothelial cell-conditioned medium (P < 0.05), which suggested viability antagonism by glucocorticoids. After 24 h of culture, eosinophil viability for replicate cells in enriched medium alone or with 1 pM GM-CSF decreased from means of 43 and 75% to means of 21 and 54%, respectively, when dexamethasone was included (P < 0.05). However, 10 pM GM-CSF, IL-3, or IL-5 protected the cells against dexamethasone and against endonuclease-specific DNA fragmentation. In this model system of eosinophil-tissue interactions, dexamethasone prevents the endothelial cells from inducing a pathobiologic phenotypic change in the eosinophil by suppression of GM-CSF elaboration to concentrations that are not cytoprotective. Cytokine priming by GM-CSF, IL-3, or IL-5 may account for the differential responsiveness of select eosinophilic disorders to glucocorticoids.