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 precu rsors and encode polypeptide chains associated in a mu-pseudo light ch ain (mu-Psi L) complex which is thought to regulate some early steps o f B cell differentiation. We have generated anti-Vpre-B monoclonal ant ibodies which allowed us to identify different steps of differentiatio n from the pro-B to the immature B cells by following surface expressi on of Vpre-B, mu and light chains in normal adult human bone marrow. A lready present at the surface of a small fraction of B cell progenitor s (CD34(+)/CD19(+)) the Vpre-B molecule was consistently found coexpre ssed with CD19 and was also found with the sequentially occurring CD10 , CD20, CD21, CD22 and CD5 markers. Three discrete cell types were ide ntified: (i) a subpopulation expressing Vpre-B without mu and which re presented an early stage of differentiation, (ii) a minor subpopulatio n co-expressing Vpre-B and mu without the conventional light chains an d (iii) a major subpopulation co-expressing Vpre-B, mu and kappa or la mbda chains, considered an intermediate pre-B/B stage. The presence of the Psi L chain in various cell subpopulations, in possible associati on with discrete molecules and/or different contexts, suggests its inv olvement at several steps of early B cell differentiation.