Résumé
In human preB cells, the μ chain is associated with a surrogate light chain composed of the VpreB and λ-like gene products. Using anti-peptide antibodies directed against VpreB and λ-like epitopes, we identified the discrete components of the μ-ψL (pseudo-light) chain complex in various preB cell lines, and in intermediate preB-B cells that co-expressed the ψL and the x chain. The λ-like gene product was identified as a single band at 20 kDa, disulfide linked to the μ chain. VpreB was detected at 16 kDa and, depending upon the cell lines, an isoform of this polypeptide was also present at 15 kDa. In addition, λ-like-VpreB chain complexes not associated with μ were identified both in cell lysates and culture supernatants. Pulse-chase experiments indicated that VpreB was transiently associated with two new polypeptides of molecular weights 17.5 and 36 kDa. Expression of μ-ψL and co-expression of μ-ψL and μL at the surface of preB and intermediate preB-B cells respectively was detected by cytofiuorimetry. The signal transduction ability of the complex in both types of cells was shown by measuring the calcium mobilization and the phosphorylation of tyrosyi residues upon stimulation by antl-μ. Signal events were similar in both cases, but differed from those induced in a mature B cell line.This points to a definite function of the preB cell receptor and suggests that the intermediate preB-B cell line still lacks some molecular components that condition initiation of a mature B cell transduction signal.