Alterations in peripheral B cells and B cell progenitors following androgen ablation in mice

The production of B lymphocytes is regulated in part by physiologic levels of androgens and estrogens. While these sex hormones down-regulate B lymphopoiesis, augmentation of B lymphopoiesis occurs under conditions where androgen or estrogen levels are decreased. In this study we examine the effect of androgen ablation of male mice on B lymphopoiesis and on the phenotypic composition of peripheral B lymphocyte populations. Spleen and thymic weights are significantly increased following castration, as is the total number of peripheral blood lymphocytes. However, the absolute numbers of B cells in the periphery are selectively increased following castration; the numbers of T cells, NK cells and granulocytes remain unchanged. The increase in circulating B cells is due largely to increases in the numbers of recent bone marrow emigrants expressing a B220(lo+)CD24(hi+) phenotype and these cells remain significantly elevated in castrated mice for up to 54 days post-castration. Similar increases in the percentages of newly emigrated B cells are observed in mice that lack a functional androgen receptor (TFM:). Finally, assessments of B cell progenitors in the bone marrow revealed significant increases in the relative numbers of IL-7-responsive B cell progenitors, including cells in Hardy fractions B (early pro-B cells), C (late pro-B cells), D (pre-B cells) and E (immature B cells). These findings demonstrate that androgen ablation following castration significantly and selectively alters the composition of peripheral B cells in mice. Further, these alterations result from the potentiating effects of androgen ablation on IL-7-responsive pro-B cell progenitors.