Pre-B cells; normal and abnormal development.

The immediate precursors of B lymphocytes have been recently identified in fetal liver and in bone marrow. Immunoglobulin genes, first of the heavy-chain gene family and later from one of the light-chain gene families, are selected and undergo functional rearrangements on one of each chromosomal pair during this stage of differentiation. Thus clonal diversity is generated among cycling pre-B cells that lack the surface antibody expression which characterizes their B-cell progeny. While the number of discriminating markers for pre-B cells is still limited, examination of bone marrow pre-B cells containing cytoplasmic mu chains but lacking surface immunoglobulin has already revealed an informative spectrum of early differentiation defects in antibody deficiency diseases and malignancies of B lineage.