CELL-SURFACE EXPRESSION OF SURROGATE LIGHT-CHAIN (PSI-L) IN THE ABSENCE OF MU ON HUMAN PRO-B CELL-LINES AND NORMAL PRO-B CELLS

Surrogate light chains (Psi L) encoded by lambda-like (lambda 5) and V preB genes play a critical role in controlling the early steps of B ce ll differentiation. We prepared new anti-VpreB monoclonal antibodies ( mAb) (3C7/6F6) which preferentially recognize the VpreB epitope at the cell surface of human cell lines that do not express the mu chain. Th ese mAb provide the first characterization of human pro-B cell lines e xpressing surface Psi L. We demonstrate that surface Psi L expression is considerably enhanced upon interleukin-7 stimulation and that the P si L complex is formed independently of the Ig alpha/Ig beta heterodim er. Finally, using these antibodies, we confirm the existence of a nor mal pro-B cell population in human adult bone marrow. Thee cells are C D34(+)CD38(+)Psi L(+), do or do not express CD19, CD10, or both epitop es, and may represent the earliest cell population committed to B cell differentiation.