Abstract
We obtained eight different cell lines in the long-term bone marrow culture system that
showed a germ-line configuration of the joining (J) region segments of the Ig heavy-chain
(IgH) genes. Their surface markers were CD45R+, Ly-1+, Lyb-2+, cIgM-, sIgM-, Ia-, Thy-1-,
Mac-1-, and IL-2R (Tac)+. Use of very young mice and the presence of IL-5 were important for preferential promotion of the survival of B-lineage lymphocytes bearing the Ly-1
markers. When we treated two of them (J8 and J10) with 5-azacytidine for 24 h followed by
co-culture with stromal cells and IL-.5, they became Ly-1+, sIgM+ B cells, and Ly-1+, Mac-1+
macrophagelike cells, respectively. After other early lymphoid lines (J1, J8, and J13) were
maintained by co-culture with ST2 and IL-5 for more than a year, they showed a heterogeneous
DNA rearrangement profile of the J region segment of the IgH gene, although only
J13 rearranged the