Generation and regeneration of cells of the B-lymphocyte lineage.

B lymphopoiesis in the mouse and in man can be divided into two phases, one in which the compartments of the B lineage are filled with cells, and a second in which these compartments are maintained by regeneration, turnover and selection. Once the immune system has been built it contains around 5 x 10(8) and 10(12) cells of the B-lymphocyte lineage in the mouse and in man, respectively, of which nearly 10 per cent are precursors that are active in regeneration, whereas over 90 per cent are resting, mature B cells.