Estrogen Deficiency Stimulates B Lymphopoiesis in Mouse Bone Marrow

We have found that an estrogen deficiency causes a marked increase in bone marrow cells. To examine the effect of estrogen on hemopoiesis, we characterized the increased population of bone marrow cells after ovariectomy (OVX). In OVX mice, the percentage of myeloid cells and granulo-cytes was decreased, whereas that of B220-positive B lym-phocytes was selectively increased 2-4 wk after surgery. The total number of myeloid cells and granulocytes did not change appreciably, but that of B220-positive cells was greatly increased by OVX. When OVX mice were treated with estrogen, the increased B lymphopoiesis returned to normal. B220-positive cells were classified into two subpopu-lations, B220I0W and B220i9'h. The majority of the B220'W cells were negative for the IgM,u chain, whereas most of the B220"'4 " cells were,i-positive. OVX selectively increased the precursors of B lymphocytes identified by B2201w.,u-negative phenotype, suggesting that an estrogen deficiency stimulates accumulation of B lymphocyte precursors. When bone marrow-derived stromal cells (ST2) were pretreated with estrogen then co-cultured with bone marrow cells in the presence of estrogen, the stromal cell-dependent B lym-phopoiesis was greatly inhibited. The present study suggests that estrogen plays an important role in the regulation of B lymphocyte development in mouse bone marrow. (J. Clin