Figure 1.

B lymphopoiesis in FLOC is unaffected by estrogen. Fragments of 15-dpc fetal liver (FL) from C57BL/6J mice were cultured for 6 days in the presence of medium alone, 17β-estradiol (10⁻⁴ M), or dexamethasone (10⁻⁸ M). Flow cytometry was performed on the recovered cells, as well as suspensions of the initial fetal liver with the indicated mAbs. The regions of the contour plots containing newly formed B cells are marked with boxes (percentages are indicated above the boxes). Before culture, fetal liver lacked CD45R⁺ IgM⁺ B cells (Upper Left), but these cells emerged during 6 days of organ culture (Upper Right, 0.16 ± 0.01 × 10⁶ B cells per fragment). In three independent experiments, B cell production was unaffected by inclusion of estrogen (Lower Left, 0.18 ± 0.01 × 10⁶ B cells per fragment), whereas it was always totally suppressed by the synthetic glucocorticoid dexamethasone (Lower Right, <0.01 × 10⁶ B cells per fragment).