Early B-lymphocyte precursors and their regulation by sex steroids

This review describes an improved characterization of early B-lymphocyte pr ecursors in mice and the remarkable sensitivity of the same cells to hormon es. The nuclear enzyme terminal deoxynucleotidyl transferase (TdT) was used as a marker to image and characterize bone marrow cells lacking all lineag e-associated markers. Most early TdT(+) precursors have a distinctive densi ty of c-kit and express the interleukin-7R alpha chain, as well as flt-3/fl k2, but lack CD34. An understanding of those cell surface properties made i t possible to obtain highly enriched, viable cells with the potential to gi ve rise to CD19(+) lymphocytes in culture. A series of other flow cytometry and culture experiments suggested a possible differentiation sequence for these early pro-B cells. This new model was used to advantage in our studie s of sex steroids, it appears that early precursors represent a hormone-sen sitive control point fur determining numbers of new B lymphocytes that are produced within bone marrow. We also compare and contrast these findings wi th B lymphopoiesis in humans.