CD19⁺ cells in the midgestation mouse embryo.

(A) Dot plots obtained after 2-color FACS analyses with biotinylated anti-B220 and anti-CD19 mAbs versus FITC anti–c-kit mAb in 11- to 12-dpc AGM-, liver-, and blood-derived cell suspensions. After Fc blocking and PI exclusion of dead cells, specific mAb signals were defined against those of isotype-matched, irrelevant mAbs. The windows shown include cells positive for established markers, and the numbers above the graphs are means ± SD of 5 independent FACS analyses/sample. (B) Absolute cell recoveries in 11- to 13-dpc AGM (▵) and FL (●). Total cells, AA4.1⁺, and CD19⁺ cells/organ are shown, the latter 2 obtained from their relative numbers in FACS analyses and absolute cell numbers/organ. n = 5-7 independent analyses; means ± SD are shown. (C) CD19 gene transcripts detected in the displayed lymphohematopoietic sites at 8 and 11 dpc. The data are presented as in Figure 1A. ST2 stromal cells were used as negative control. n = 4 independent samples. (D) Surface phenotype of 11-dpc CD19⁺liver cells. The 2-color FACS analyses were done with biotinylated anti-CD19 mAb versus the FITC mAbs specific for the shown receptors. White and shaded histograms represent negative and specific signals, respectively, obtained from gated CD19⁺cells.