B lymphocyte differentiation from fetal liver stem cells in89 Sr-treated mice1

89Sr treatment was used to determine if stem cells in young fetal liver could differentiate to mature B lymphocytes in adult animals that lacked functional bone marrow. Isotope injection alone resulted in a severe and lasting depletion of bone marrow cells and particularly lymphocytes, multipotential stem cells, and progenitors for granulocytes and macrophages. The latter two functional populations of cells expanded in number in the spleen but not the liver after their destruction in bone marrow. The total body content of stem cells did not, however, return to normal. Spleen B cells and lymphocytes lacking B or T cell markers were reduced by 89Sr treatment and possible reasons for this depletion are discussed. B lymphocytes were formed in lethally x-irradiated mice that had less than 1% of normal bone marrow function after reconstitution with fetal liver cells. These cells were immunologically mature by virtue of their ability to mount a primary immune response and function in a thymus-independent adoptive anti-hapten response.