The κ-like pre-B receptor: Surplus biology or a missing link?

After the demonstration that surrogate JCκ polypeptides could covalently bind μ heavy chain and upon the characterization of the Vκ-like component of the κ-like pre-B cell receptor, it became evident that germline transcription is not sterile. The present review discusses the concept of the alternative usage of κ-like pre-B cell receptors and classical pre-B cell receptors utilizing the λ-like surrogate light chain composed of λ5 and VpreB. We propose that both κ-like and λ-like pre-B cell receptors work in concert in a fail–safe mechanism to promote light chain rearrangement, heavy chain allelic exclusion and B-lymphocyte maturation.