Kinetics of sequential appearance of IgM and IgD on B lymphocytes in the bone marrow of the adult mouse.

The relationship between the expression of IgM, and IgD at the B-cell surface, was examined in the adult murine bone marrow. Groups of mice were injected with hydroxyurea, which prevents DNA synthesis by blocking the production of deoxyribonucleotides. The numbers of cells per femur, expressing either IgM alone or in conjunction with IgD were followed at 24 hr intervals after the drugs administration. Other mice were injected with tritiated thymidine over an 8 hr period. The appearance of radioactive label within cells expressing IgM alone or with IgD, was followed over a 5 day period. Both sets of results showed that IgM bearing cells were derived from a rapidly dividing precursor cell pool, by a process which takes more than 24 hr and does not require DNA synthesis. Cells expressing IgM and IgD together were also produced from rapidly dividing precursors. This developmental process takes more than 48 hr, does not require DNA synthesis and may go via an intermediate stage namely the cell expressing IgM alone.