Induced up-regulation of the membrane-bound hIL-5R isoform by IL-5.

(A) Flow cytometry plots of FDC-P1-MINI-1.1 cells labeled with the lipophilic chromophore PKH2-GL. Cell growth in human IL-5 (bottom panel) showed a single population, which parallels spontaneous autocrine outgrowth (middle panel). If a fast proliferating subpopulation were present, dilution of the fluorescent dye would be much more pronounced and would approach fluorescence intensities as shown for cells grown in IL-4-containing medium (top panel). Representative of 2 independent experiments. (B) RT-PCR analysis of IL-5Rα isoform mRNA expression by FDC-P1-MINI-1.1 cells grown in medium containing EL4 CM, IL-5 alone, IL-4 alone, or IL-4 and IL-5 combined. The upper part of each panel shows the products of a competitive PCR; the lower part represents PCR data using primers for the TM-transcript only. TM-transcripts are detected in the presence of IL-5, but also, although at a lower level, and with slower kinetics in the presence of IL-4 plus IL-5. Representative of 2 independent experiments. (C) FDC-P1-MINI-1.1 cells transfected with the pSVZeo-mIL-5Rα vector, which directs the expression of the murine IL-5Rα subunit, will grow in the presence of murine IL-5, independent of hIL-5. Under these conditions, switch of isoform expression of hIL-5Rα transcripts from the minigene was also observed (arrow). Sampling time points are shown. Representative of 2 independent experiments.