Bipotential precursors of B cells and macrophages in murine fetal liver.

LYMPHOCYTES (B and T cells) derive continuously from the same multipotential stem cells that produce myeloid cells, including erythrocytes, granulocytes and macrophages. Tri- and bipotential myeloid intermediates between the multipotential stem cells and later unipotential cells have been identified using clonal methods in culture. Although similar methods have detected committed pre-B cells in mouse fetal liver, earlier progenitors with additional non-B lineage options have not been demonstrated in normal tissues. We report the characterization and purification of fetal liver cells that generate clones containing both macrophages and B cells, identified biochemically and morphologically. The common origin of the two cell types was shown by culture of single precursor cells. Their dual potential and unrearranged immunoglobulin loci place the precursors before exclusive B-lineage commitment in the haematopoietic hierarchy. The availability of such cells in purified form will allow direct study of lineage choice in cells having both lymphoid and non-lymphoid options.