PREGNANCY - A CLUE TO NORMAL REGULATION OF B-LYMPHOPOIESIS

The large-scale production of lymphocytes in the bone marrow reflects a delicate balance between positive and negative regulatory signals. F or instance, interleukin 7 (IL-7) provides a positive signal, and appe ars to be both essential and limiting in the mouse. However, much less is understood concerning the negative molecular signals that may limi t the output of lymphocytes. Here, Paul Kincade and colleagues discuss how a chance observation with pregnant mice revealed that sex steroid s can act as negative regulators of B lymphopoiesis, and may do so und er normal steady-state conditions.