Myelogenous production and maturation of B lymphocytes in the mouse.

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Abstract
Cells of the B lymphocyte lineage in young adult murine bone marrow were identified and resolved into compartments based on cell size and the expression of the mu heavy chain of IgM in the cytoplasm (cmu) or on the cell surface (smu). The proliferative status, renewal rate, and intercompartmental transit of cells through the defined compartments were determined using established protocols of in vivo tritiated thymidine (3H-TdR) administration, followed by radioautography of bone marrow smears. In addition, we specifically tested whether any of the defined cell compartments were derived from long-lived lymphocytes that are known to enter the marrow. Only large cells immediately incorporated the DNA precursor and both small cmu+ smu- and cmu+ smu+ cells were postmitotic lymphocytes. Large cmu+ smu- cells were found to be a rapid transit compartment in which the last mitosis of B lymphocyte differentiation takes place. All large cmu+ smu- cells divided only once, and both daughter cells entered the postmitotic small cmu+ smu- population. Large cmu+ smu- cells relied for their maintenance entirely on cell input from an Ig- progenitor compartment. Progenitors of cmu+ smu- large cells were not small lymphocytes, proliferated less rapidly than their descendants, and maintained the input of large cmu+ smu- cells for up to 40 hr. Approximately 70% of small cmu+ smu- cells were the immediate division products of large cmu+ smu- cells, whereas the remainder were derived from a precursor with no detectable mu synthesis. Small cmu+ smu+ cells were the maturation products of small cmu+ smu- cells. This conversion appeared to take place at random rather than as a function of postmitotic age. Renewal times for small cmu+ cells without or with detectable smu were calculated to be 48 and 96 hr, respectively. Only the cmu- smu+ compartment included long-lived cells. All other mu+ populations either proliferated or were replaced by newly produced cells. A conspicuous minor population of large smu+ B cells were detected, and the data relating to these were subjected to several interpretations. These observations provide insight into the origin and fate of B lineage precursors in the marrow and suggest a scheme for the terminal stages of B lymphocytes formation that is similar to the myelogenous production of other hemopoietic cells.