ADULT BONE-MARROW CONTAINS PRECURSORS FOR CD5(-CELLS() B)

To determine directly whether B cell precursors of adult origin are ca pable of generating CD5(+) B cells, we reconstituted neonatal C3H.SCID mice with adult C57BL/6 bone marrow and analyzed splenic B cells 10 m onths later. Surface staining and flow cytometry revealed that the B c ells were of donor origin and that 30 % were CD5(+). This confirms tha t in vivo generated CD5(+) B cells can be adult derived. After anti-Ig M (but not lipopolysaccharide) stimulation in vitro, virtually all of the B cells from the bone marrow-reconstituted mice expressed surface CD5. Sequence analysis of expressed V(H)DJ(H) genes from the CD5(+) B cells present after anti-IgM stimulation revealed a high frequency of N nucleotide addition in CDR3 regions. The presence of N nucleotides i ndicates that these sequences were derived from CD5(+) B cells of adul t origin rather than from long-lived fetal precursor B cells present i n either the adult bone marrow at the time of transfer or adult spleen . These experiments demonstrate conclusively that adult bone marrow co ntains precursors for CD5(+) B cells and that unlike fetal liver-deriv ed precursors these express terminal deoxynucleotidyl transferase.