Figure 2.

Progenitors from fetal liver, but not adult marrow, generate B lineage cells in the presence of estrogen. Bone marrow (BM) cells from 8-week-old C57BL/6J mice and fetal liver (FL) cells from 15 dpc embryos were harvested, enriched for lineage-negative cells, and sorted as Lin⁻ c-kit^Lo cells on the MoFlo. These highly enriched precursors were then cultured for 7 days under stromal cell-free, serum-free conditions in the presence of medium alone, 17β-estradiol (10⁻⁸ M) or dexamethasone (10⁻⁸ M). Recovered cells were evaluated by flow cytometry. Lymphoid progenitors from either bone marrow or fetal liver gave rise to CD19⁺ B lineage cells in stromal-cell-free, serum-free cultures (Top, 10.7 ± 0.26 × 10³ CD19⁺ cells per marrow precursor culture, and 1.84 ± 0.16 × 10³ CD19⁺ cells per fetal precursor culture). In two independent experiments, estrogen blocked B lineage differentiation from adult (Left Middle, 0.17 ± 0.03 × 10³ CD19⁺ cells per marrow precursor culture), but not fetal (Right Middle, 2.26 ± 0.14 × 10³ CD19⁺ cells per fetal precursor culture) progenitors. The synthetic glucocorticoid dexamethasone totally blocked generation of CD19⁺ lymphocytes and induced CD11b/Mac-1⁺ myeloid lineage cells regardless of the source of precursors (Bottom, < 0.07 × 10³ CD19⁺ cells recovered per culture).