Platelet-activating-factor-induced augmentation of production of eosinophil-lineage cells in hematopoietic precursor cells obtained from human umbilical cord blood.

Platelet-activating factor (PAF)-induced augmentation of spontaneous differentiation into eosinophil-lineage cells from hematopoietic precursor cells was found among human umbilical cord blood mononuclear cells (CBMCs). This ability of PAF to augment eosinophil production was significantly (p < 0.01) inhibited by the addition of the anti-PAF agent WEB 2086. This enhancing effect of PAF was significantly (p < 0.01) diminished by the presence of antibodies to interleukin (IL)-1 alpha, -beta and IL-3, whereas antibodies to IL-5 or granulocyte-macrophage colony-stimulating factor (GM-CSF) did not diminish it. IL-1 beta, IL-3 or IL-5 gene expression was detected in cellular RNA isolated from both medium- and PAF-stimulated CBMCs using the reverse transcription polymerase chain reaction (RT-PCR) method; however, no expression of GM-CSF was detected. Moreover, 5 times as much IL-3 was detected in the PAF-stimulated CBMC culture supernatant than in that of cells treated with the medium. In the case of IL-1 beta, there was no difference between the 2 cell preparations. On the other hand, no IL-5 or GM-CSF was detected in the supernatant after stimulation with medium or PAF. Depletion of CD2+, CD16+ or CD19+ cells, but not CD14+ cells, from CBMCs resulted in a marked decrease in PAF-induced augmentation of eosinophil production. These results suggest that PAF induces the augmentation of IL-3 production in CBMCs which in turn enhances differentiation into eosinophil-lineage cells.