Differential effect of an Ig μ transgene on development of pre-B cells in fetal and adult SCID mice

Progression of pro-B lymphocytes to the pre-B stage depends on the expression of a pre-B cell receptor (pre-BCR), consisting of an Ig μ H chain, Ig surrogate light chain, and associated signal transducing chains. Mice that are unable to express a pre-BCR show an arrest of B cell development at the pro-B stage. Such is the case for severe combined immune deficient (SCID) mice in which μ chains are not made because of a defect in V(D)J recombination. When μ chains are made, as in SCID mice bearing a functional μ transgene, then B cell differentiation can proceed to the pre-B stage. However, as reported here, a μ transgene (M54) that promotes development of SCID pre-B cells in adult bone marrow fails to do so in fetal liver. We suggest that a pre-BCR containing the M54 μ chain cannot signal progression of pro-B cells to the pre-B stage in the fetal liver microenvironment.