A novel anti-Vpre-B antibody identifies immunoglobulin-suprogate receptors on the Surface of human pro-B cells

V pre-B and lambda 5 genes, respectively, encode V-like and C-like domains of a surrogate immunoglobulin light chain (Psi L). Such Psi L complex is expressed in early progenitor B (pro-B) cells, before conventional immunoglobulin heavy (mu H) and light (L) chains are produced. We raised a wide panel of monoclonal antibodies (mAbs) against soluble recombinant V pre-B proteins to study early events in human B cell development. One of these antibodies, B-MAD688, labeled surrogate Ig-complexes on the surface of mu H- pro-B cell lines and normal bone marrow cells in immunofluorescence assays. Immunoprecipitations using surface-labeled pro-B cells and B-MAD688 mAb indicated that human Psi L is associated with high molecular weight components homologous the surrogate heavy (Psi H) chains described in mouse. Using B-MAD688 and SLC2 mAbs, we were able to distinguish between Psi H Psi L and mu H Psi L complexes on the surface of human pro-B and later precursor, pre-B, cells. The finding of Psi H Psi L complexes in mouse and man lead us to hypothesize a role for Psi H-containing receptors in B cell development.