Chronic treatment of mice from birth with anti-µ antibodies aborts development of B lymphocytes and plasma cells. In these studies we show that bone marrow from anti-µ-treated mice contains a population of cells with cytoplasmic IgM, but which lack detectable cell-surface IgM. These cells are analogous to pre-B cells, defined in ontogenetic studies as the immediate precursors of B lymphocytes. Pre-B cells from bone marrow of anti-µ treated mice retain their functional integrity, as evidenced by their ability to give rise to sIgM+, LPS-responsive lymphocytes in culture. We also show that cyclophosphamide treatment destroys pre-B cells and that recovery of pre-B cells in bone marrow precedes the regeneration of sIgM+ B lymphocytes. Generation of B lymphocytes in adult mice apparently occurs exclusively in the bone marrow because induction of extramedullary hemopoiesis in spleen was not accompanied by the appearance of pre-B cells in that organ.
This work was supported by Grants CA 16673 and CA 13148 awarded by the National Cancer Institute and Grant AI 11502 awarded by the National Institute of Allergy and Infectious Diseases.