Effects of gonadectomy and testosterone on lymphocytes in the bone marrow of the mouse: an electron microscopic study

Effects of gonadectomy and testosterone on lymphocytes in the mouse marrow were studied quantitatively by electron microscopy. Marrow lymphocytes rapidly decreased in frequency after puberty in normal males, but increased after removal of the testes. In castrated males, testosterone administration resulted in a reduction in the percentage of marrow lymphocytes. In females, ovariectomy caused a slight but significant increase in the proportion of marrow lymphocytes. Marrow lymphocytes were, for the most part (about 97%), composed of small lymphocytes, which were distinguishable as dark and light types. In adult controls, light small lymphocytes made up the greater portion of marrow small lymphocytes, whereas in gonadectomized mice dark small lymphocytes constituted the majority of marrow lymphocytes. In castrated males testosterone exerted a depressant effect on dark lymphocytes, but not on light lymphocytes, indicating that dark lymphocytes were sensitive to hormonal activity of the testis, and light lymphocytes were not.