Fig. 5. Expression of the PRL-R in mouse BM pro-B and pre-B cells. Three-color flow cytometry analyses were performed on BM cells as described in "Materials and Methods." BM cells (5 x 105) were incubated with either FITC-anti-CD43 or FITC-anti-IgM, together with PE-anti-B220 and purified mouse anti-rat PRL-R U5 mAb. This later was revealed with TC-conjugated, goat-anti-mouse immunoglobulin. Pro-B cells were defined as B220lowCD43+, and they represented 3–4% of total BM (window of the upper control plot). Pre-B cells were included in the B220highIgM23 window (8–10% of total BM; window of the bottom contour plot). Right histograms, PRL-R expression on pro-B and pre-B cell populations. Shaded histograms, background signals of isotype-matched, irrelevant mAb. The data are representative of three independent experiments. Fluorescence signals are displayed in logarithmic scales.