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, w e characterized the increased population of bone marrow cells after ov ariectomy (OVX). In OVX mice, the percentage of myeloid cells and gran ulocytes was decreased, whereas that of B220-positive B lymphocytes wa s selectively increased 2-4 wk after surgery. The total number of myel oid cells and granulocytes did not change appreciably, but that of B22 0-positive cells was greatly increased by OVX. When OVX mice were trea ted with estrogen, the increased B lymphopoiesis returned to normal. B 220-positive cells were classified into two subpopulations, B220(low) and B220(high). The majority of the B220(low) cells were negative for the IgM mu chain, whereas most of the B220(high) cells were mu-positiv e. OVX selectively increased the precursors of B lymphocytes identifie d by B220(low). mu-negative phenotype, suggesting that an estrogen def iciency 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 st romal cell-dependent B lymphopoiesis was greatly inhibited. The presen t study suggests that estrogen plays an important role in the regulati on of B lymphocyte development in mouse bone marrow.