Kinetics of B cell subpopulations in peripheral lymphoid tissues: evidence for the presence of phenotypically distinct short-lived and long-lived B cell subsets

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Abstract
A small proportion of the slg+ B lymphocytes in peripheral lymphoid organs [22% in spleen and 6 % in lymph node (LN)] in rat carries the Thy-1 antigen. These Thy-1+ B cells represent newly formed bone marrow (BM) derived (or Immature) B cells. In this study we investigated the kinetic behavior of Thy-1+ and Thy-1− B cells in various lymphoid tissues. The renewal rates of these B cells in young adult rats were determined by continuous administration of 5-bromo-2-deoxyuridine (BrdU) for up to 6 weeks. At several time intervals, Thy-1+ and Thy-1− B cell subpopulations in BM, blood, spleen and popllteal LN were analyzed for the presence of incorporated BrdU, using three-color immunocytology on cytospin preparations. In all tissues studied, the Thy-1+ B cells were rapidly renewed with a rate that varied between 58 % (BM) and 22 % (LN) per day. Virtually all Thy-1+ B cells were labeled by BrdU within a period of 8 –16 days, indicating that all these cells are relatively short-lived. By contrast, the replacement of Thy-1− B cells in these tissues was 30 –40 times lower, and ranged between 2.0 and 0.8 % per day. In absolute numbers we estimate that 57 million Thy-1+ B cells are renewed per day in the BM whereas only 10 million Thy-1− B cells are replaced in the pool of long-lived peripheral B cells. This implicates a cell loss of 80 % at the transition of the Thy-1+ to the Thy-1− B cell stage. The few B cells that actually become incorporated into the pool of mature B cells are most probably selected on the basis of the specificity of their slg.

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