Castration of normal male mice leads to splenic enlargement and expansion of the B cell population. Since the spleen does not express receptors for androgens, these changes are most likely mediated by effects of androgens on other target organs. Two potential sites of androgen-mediated effects on B cells are evaluated in these studies: thymus and bone marrow. We first confirmed other findings indicating that castration of normal male mice results in expansion in the numbers of bone marrow B cells and then extended these observations by showing that these changes were reversible following androgen replacement B cell expansion in castrate marrow and spleen was not altered by prior thymectomy, suggesting that thymic androgen receptors are not involved in the observed effects. Androgen receptors were found to be present in both immature B cells and marrow stromal cells by immunoblotting and ligand binding assays. The results suggest a direct modulatory role for androgens on B cells within the bone marrow compartment.
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