Functional assessment of precursors from murine bone marrow suggests a sequence of early B lineage differentiation events

Most lineage marker-negative (Lin(-))TdT(+) cells from murine marrow lack C D34 but display c-kit at low density as well as IL-7R alpha and FIk-2/FIt-3 receptors. Single cells with these characteristics generated CD45RA(+)CD19 (-) as well as CD19(+) lymphocytes in culture. CD45RA+CD19- marrow cells we re resolved into three nonoverlapping subsets. One subset, lacking DX5 and Ly-6C antigens, yielded CD19(+) cells in culture. Further analysis demonstr ated CD24 on most Lin(-)TdT(+) cells and all CD45R(+)CD19(-)DX5(-)Ly-6C(-) cells. Mac-1/CD11b was absent from these two subsets of B lineage precursor s, while IL-7R alpha was retained during subsequent differentiation to a CD 19(+) and stromal cell-independent stage. These findings contrast with prev ious descriptions of B lymphocyte precursors and suggest a sequence of earl y differentiation events.