Figure 1.

Early stages of B lymphopoiesis are blocked by pregnancy and estrogen treatment.

BM cells of control mice or pregnant Rag1/GFP heterozygotes were stained with the indicated Ab and analyzed in flow cytometry. Whole BM cells were stained with CD45R/B220 and CD43 (A, upper), and Lin^- cells were gated and resolved with c-kit and Sca1 staining (B, upper). The CD45R/B220⁺ CD43^Hi fraction and the LSK fraction were further resolved with Rag-1/GFP intensity (A, B, lower). The numbers in each panel are percentages of the gated population. The figures represent data obtained on day 19.5 of gestation. Rag1/GFP heterozygous males were intraperitoneally given a single injection of estrogen (1 mg/mouse) and analyzed at the indicated time after injection. BM Lin^- cells were resolved with c-kit and Sca1 (C, upper), and then the LSK fraction was further resolved according to Rag1/GFP intensity (C, lower). Cell numbers in the indicated populations were calculated (D). The data show mean ± SD values from 4 mice in each group, and the figures are representative of 2 independent trials. Significant differences from control (0h) values are indicated by an asterisk (p<0.05) or two asterisks (p<0.01). (E) BM LSK cells of estrogen-injected (at 96h after injection) or control mice were subdivided according to the expression of Flk2/Flt3 and Rag1/GFP. Splenic LSK cells of the same mice were also evaluated (F).