Mice transgenic for γ2b Ig heavy chain were examined for alterations in B-cell differentiation
and endogenous Ig gene rearrangement and expression. Fresh bone marrow from these mice
was markedly reduced in BP-1+ cells and there were small reductions in B220+ and sIg+ cells. A-MuLV (Abelson murine leukemia virus) transformants from these bone marrow cells
showed little alteration in Ig gene rearrangement and expression when compared to
controls, however. Isolation of the B-lymphoid compartment from these mice in vitro using
LBMC (lymphoid bone marrow cultures) enabled more detailed characterization of the
effects of the transgene. LBMC derived from γ2b transgenic mice had similar growth
kinetics, but a 4-5-week delay in the expression of endogenous mu Ig in comparison to
control cultures. Nucleic acids derived from these early cultures prior to endogenous mu Ig
expression showed reduced Ig JH rearrangements, some sterile mu transcription, low levels
of BP-1 expression, and virtually undetectable TdT (terminal deoxynucleotidyl transferase)
expression. Thus, this γ2b transgene appears able to affect early B-lymphocyte development.