Differentiation of embryo cell lines to CD19⁺IgM⁺ immature B cells in ST2/IL-7 cell cultures.

(A) Relative number of sIgM⁺ B cells in both embryo and LFL/BM cell lines after 1, 2, and 5 months of continuous ST2/IL-7 (3 ng/mL) cell cultures, as obtained by flow cytometry analyses. Each point corresponds to one independent cell line. The cell lines were considered IgM⁺ when containing 1% sIgM⁺ cells or more (horizontal dotted bar). The mean values of IgM⁺ B cells present in each of the IgM⁺ embryo cell lines are shown as thick horizontal lines. The average percentage of IgM⁺ cell lines found at each time point is shown in the bottom line. (B) Cell surface phenotype of IgM⁺ B cells from a representative embryo cell line cultured for 2 months. This particular cell line contained 12% B cells. The mAbs and protocols used for double stainings are described in “Materials and methods.” The forward side scatter (FSC) is displayed in a linear scale. The fluorescein isothiocyanate (FITC) and PE fluorescence intensity of the different mAbs are represented in a log₁₀ scale.