Abstract

DNA labeling by 3H-thymidine in vitro and antiglobulin- 131I binding in vitro were used to determine the development and turnover of immunoglobulin-bearing lymphocytes in mouse bone marrow. Bone marrow cells from CBA mice previously injected repeatedly with 3H-thymidine for 1–84 hr were exposed to 131I-labeled rabbit-antimouse globulin for 30 min at 0 °C, and examined radioautographically. The antiglobulin-binding cells in bone marrow were predominantly (97–98%) nondividing small lymphocytes. Some plasmacytoid and monocytoid cells, but not the proliferating large lymphoid cells, also bound antiglobulin. The 3H-thymidine labeling index of the small lymphocyte population showed a rapid exponential increase (50% in 32 hr). The first small lymphocytes to show 3H-thymidine labeling were those lacking antiglobulin-binding capacity, reaching approximately 90% 3H-thymidine labeling after 2 days. Small lymphocytes which bound antiglobulin- 131I at a concentration of 1.0 μg/ml became labeled with 3H-thymidine only after a lag of approximately 1.5 days. More avid antiglobulinbinding cells were delayed a further 12 hr in 3H-thymidine labeling. During in vitro culture the proportion of antiglobulin-binding small lymphocytes increased progressively in bone marrow but decreased in spleen cell suspensions. The results demonstrate a continuous, rapid renewal of immunoglobulin-bearing small lymphocytes in adult mouse bone marrow. Surface immunoglobulin molecules are not detectable when marrow small lymphocytes are first formed, but they appear and increase progressively in density as the cells mature.

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