Control of B-cell maturation in mice. I. Increased B-cell maturation in vitro by bone marrow protected during whole body irradiation.

The possibility of a homeostatic control on the production of B cells was studied in CBA mice following whole body irradiation (750 rads). Bone marrow cells from femurs shielded from irradiation were taken at 24 h and the number of surface immunoglobulin positive cells assessed with a fluorescence-activated cell sorter after 24 h in vitro. The cells from the irradiated shielded mice showed greater absolute number of 'bright' B cells with a high density of surface immunoglobulin (mean increase 60%--100%) than cells from control unirradiated mice. These bright B cells did not incorporate (3H) thymidine in vitro and treatment with hydroxyurea (an inhibitor of DNA synthesis) did not prevent their increase. It was concluded that the increased number of bright B cells in vitro arose from augmented maturation or differentiation and not from a proliferative process.