Using a method which allows simultaneous flow cytometric detection of cell surface markers and 5-bromo-2'-deoxyuridine (BrdU) incorporation, the distribution and proliferative behavior of B lineage subpopulations was studied in intact adult mice VSports手机版. In the bone marrow we could define two subsets of B cells on the basis of differential expression of the pan-B cell marker B220 and of membrane-associated mu and delta immunoglobulin heavy chains. B220dull mu+ delta- B cells were found to emerge from rapidly dividing cells and probably represent B cells recently generated from B220dull mu- pre-B cells. In contrast, only few, if any, of the B220bright mu+ delta+ B cells were labeled with BrdU after a period of 8 days, suggesting that these cells represent long-lived B cells residing in the bone marrow. Analysis of BrdU-incorporation into splenic B cells showed that only 20% of these cells had gone through cell division during the preceding 8 days. Almost none of the B cells in the peritoneum, a large fraction of which belongs to the Ly1 B subset, were labeled with BrdU over a period of 7 days in 8-month-old animals. .