Both NK-and B-lineage lymphocytes derive from hormone-sensitive progenitors in the bone marrow.

Lin⁻ c-kit^Lo bone marrow cells were prepared from mice implanted 7 days previously with estrogen pellets (β-estradiol–treated mice) or from control animals (control mice) and used to initiate cultures containing SCF, FL, IL-7, and IL-15. (A) The top panels show typical flow cytometry profiles for cells harvested 7 days later. (B) The data were also calculated according to absolute numbers of B-lineage (open bars) or NK-lineage (hatched bars) cells generated in culture per input cell.