λ5 is required for rearrangement of the Ig κ light chain gene in pro-B cell lines

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Abstract
λ5 associates with Vpre-B to form the surrogate light (L) chain. The phenotype of λ5 knockout mice showed severe impairment of B cell development from pro-B to immature B cell stages. To investigate the function of the surrogate L chain at this stage, we restored expression of λ5 to λ5-deficient pro-B cell lines which were established from bone marrow cells of λ5 knockout mice in the presence of IL-7 and a stromal cell line. Some of these lines are severely impaired in B cell development from pro-B to immature B cell stages as is seen in vivo in λ5 knockout mice. Restoration of λ5 protein by retroviral-mediated gene transfer into established λ5-deficient pro-B cell lines induced rearrangement of the Ig κ L chain genes after removal of IL-7 from the culture. Immunoprecipitation revealed that the restored λ5 in the cell line is coupled with Vpre-B to form the surrogate L chain. The results demonstrate that formation of a complete surrogate L chain, consisting of both λ5 and Vpre-B, stimulates efficient rearrangement of the κ L chain genes.