Characterization of a B Cell Progenitor Present in Neonatal Bone Marrow and Spleen But Not in Adult Bone Marrow and Spleen

Abstract

The neonatal period marks an important time in mammalian immunologic development, yet it is often ignored in studies of lymphocyte development. We identified a cell population with the phenotype heat stable Ag (HSA)low lin− CD43low that contained B cell progenitors at a high frequency in the neonatal bone marrow and spleen. Although cells with a similar phenotype can be identified in the bone marrow and spleen of adult animals, these populations showed a greatly reduced frequency of B cell progenitors. B lineage cells were detected after 7 days in culture at a frequency of 1:15 when HSAlow lin− CD43low cells from neonatal bone marrow were cultured on stromal cells and IL-7 under limiting dilution conditions. Under similar conditions, the equivalent population in adult bone marrow had a frequency of B cell progenitors that was less than 1:2000. The expression of terminal deoxynucleotidyl transferase in freshly sorted neonatal HSAlow lin− CD43low cells suggested that cells committed to the lymphocyte lineage were present in this population. These data suggested that the HSAlow lin− CD43low population of cells represents a pool of B lineage precursors that may be responsible for filling the immune compartment early in neonatal life.