Phenotypic and functional characterization of murine B lymphocyte precursors isolated from fetal and adult tissues.

Murine fetal liver and adult bone marrow cells identified by monoclonal 14.8 antibody were enriched on antibody-coated polystyrene petri dishes. Cell surface immunoglobulin (sig)-bearing cells were depleted before this enrichment procedure, and the resulting preparations of 14.8+, slg- cells were characterized as to morphology, immunoglobulin gene expression, and functional potential in vivo and in vitro. All cells with detectable mu chains of IgM in the cytoplasm (cmu) were found to be included in the 14.8+ population. The enriched cells did not contain significant numbers of committed granulocyte-macrophage progenitor cells or putative hemopoietic stem cells. Selected cells from 16-day fetal liver were large, a majority of the cells had a lobulated rather than a spherical nuclear outline, and less than 1% had detectable cmu. Enriched cells from 19-day fetal liver were on the average smaller than those from 16-day-gestation liver and had a more typical lymphoid morphology; 30% were cmu+. Adult bone marrow 14.8+, slg- cells were similar to 19-day fetal liver cells in morphology, and approximately half were cmu+. These selected precursor cells retained the capacity to mature in vivo and in vitro. Fetal and adult 14.8+, slg- cells were efficient in generating newly formed B cells in vivo, and this maturation step appeared to be dependent on the presence of microenvironmental accessory cells. However, the ability of positively selected cells to mature in vitro was markedly decreased, and this potential was not rescued by providing known sources of accessory cells. Possible reasons for this difference are considered. This technique for positively selecting cells has allowed us to directly compare for the first time B cell precursors from fetal and adult tissues and will be invaluable for resolution of the cell compartments in the differentiation of B lymphocyte precursors, in the study of accessory cells known to facilitate this process, in the definition of humoral factors which may act on pre-B cells, in the study of immunoglobulin gene rearrangements which take place during normal differentiation, and for further comparative studies of fetal and adult lymphopoiesis.