Differentiation of B Lymphocytes from Stem Cell Precursors

Summary

The ready capacity of mouse B lymphocytes to bind ¹²⁵I-labeled anti-globulin has been used as a marker for a lymphocyte’s B cell status. Fetal liver stem cells lack this marker, and have been used to reconstitute lethally irradiated animals. When 2 x 10⁶ fetal liver cells are injected, and the spleens of the host mice are monitored for appearance of B cells, it is seen that no reconstitution occurs before 8 days. This is surprising, as erythropoiesis and myelopoiesis are by then proceeding very rapidly. After eight days, repopulation occurs exponentially, with a doubling of the B cell content each 1. 5 days. Reconstitution is complete only three to four weeks after irradiation. Functional reconstitution of the immune response to DNP-flagella follows a basically similar but slightly slower pattern.

B cell differentiation has also been monitored in embryo mice. B cells were first noted at day 16.5 of gestation in both blood and spleen, though representing only 0. 1 to 0. 3% of the white cell population. They were noted slightly later in the fetal liver. Numbers rose rapidly in all organs, so that at birth 2 to 7% of blood and spleen cells and 1% of fetal liver cells were B cells. The total number of B cells in the mouse at birth was estimated to be 100,000 to 200,000. The future use of B cell differentiation models in studies of the induction of immunological tolerance is discussed.