DISCRETE EARLY PRO-B AND PRE-B STAGES IN NORMAL HUMAN BONE-MARROW AS DEFINED BY SURFACE PSEUDO-LIGHT CHAIN EXPRESSION

Vpre-B and lambda-like genes are selectively expressed in B cell precursors and encode polypeptide chains associated in a mu-pseudo light chain (mu-Psi L) complex which is thought to regulate some early steps of B cell differentiation. We have generated anti-Vpre-B monoclonal antibodies which allowed us to identify different steps of differentiation from the pro-B to the immature B cells by following surface expression of Vpre-B, mu and light chains in normal adult human bone marrow. Already present at the surface of a small fraction of B cell progenitors (CD34(+)/CD19(+)) the Vpre-B molecule was consistently found coexpressed with CD19 and was also found with the sequentially occurring CD10, CD20, CD21, CD22 and CD5 markers. Three discrete cell types were identified: (i) a subpopulation expressing Vpre-B without mu and which represented an early stage of differentiation, (ii) a minor subpopulation co-expressing Vpre-B and mu without the conventional light chains and (iii) a major subpopulation co-expressing Vpre-B, mu and kappa or lambda chains, considered an intermediate pre-B/B stage. The presence of the Psi L chain in various cell subpopulations, in possible association with discrete molecules and/or different contexts, suggests its involvement at several steps of early B cell differentiation.